Unexpected Formation and Structural Characterization of a Dinuclear Sodium Half-Sandwich Complex

Treatment of N,N′-diisopropylcarbodiimide with sodium cyclopentadienide (NaCp) in a molar ratio of 1:1 in THF solution resulted in formation of the unexpected dinuclear sodium half-sandwich complex [NaC5H3{C(NHPr)(=NPr)}2-1,2]2 (1) as colorless crystals in low yield. The newly formed ligand, which belongs to the group of 6-aminofulvene-2-aldiminate ligands, coordinates to sodium in an η5-coordination mode via the cyclopentadienyl ring. Dimerization occurs through additional chelating κN,N′-coordination of the amidine substituents. The NMR data of 1 indicated a slow dimer/monomer equilibrium in solution. A serendipitously isolated hydrolysis product, {μ-(PrNH)2C=O}2[NaC5H3{C(NHPr)(=NPr)}2-1,2]2 (2), contains the new 6-aminofulvene-2-aldiminate ligand in the N,N′-chelating coordination mode with the cyclopentadiene ring being uncoordinated. In this case, dimerization occurs through the presence of two bridging neutral N,N′-diisopropylurea ligands. Both compounds have been structurally characterized by single-crystal X-ray diffraction.


Results and Discussion
The reaction of 1 equiv. of sodium cyclopentadienide, NaCp, with N,N′-diisopropylcarbodiimide was carried out in THF solution at room temperature and resulted in formation of a clear, light-brown solution.Removal of the solvent, followed by extraction with n-pentane, provided a yellow solution besides a large amount of insoluble brown material.All attempts to crystallize the latter from diethyl ether or THF failed.Crystallization of the n-pentane filtrate at 4 °C afforded colorless, needle-like crystals in low yield.An IR spectrum of the product suggested that the expected simple addition reaction (Scheme 3a) had not taken place, as it showed three bands typical for NH functional groups at ν 3436 m (νas NH), 3386 m (νs NH), 3223 m (νs NH).A single-crystal X-ray diffraction study revealed the formation of an unexpected dimeric sodium half-sandwich complex [NaC5H3{C(NH i Pr)(=N i Pr)}2-1,2]2 (1).As illustrated in Scheme 3b, the bis(amidino)-substituted cyclopentadienyl anion [C5H3{C(NH i Pr)(=N i Pr)}2-1,2] − had formed through double addition of N,N′-diisopropylcarbodiimide to the cyclopentadienyl ring.With ca.9% (determined after the crystal structure had been elucidated) the isolated yield of 1 was reproducibly low, although synthetically useful amounts (>1 g) could be easily prepared.Notably and surprisingly, the isolated yield of 1 could not be improved by carrying out the reaction of NaCp with N,N′-diisopropylcarbodiimide in a 1:2 molar ratio as suggested by the composition of the products.Several experiments using 2 equiv. of i PrN=C=N i Pr under different reaction conditions afforded only small amounts of NaCp as the only crystalline material.Making the amidinate and guanidinate ligands extremely versatile, the substituents at all three atoms of the N-C-N backbone can be varied.A generally applicable synthetic route to lithium amidinate precursors involves the addition of organolithium reagents to N,N -disubstituted carbodiimides, as shown in Scheme 2. The substituents R and R can be varied in a wide range and, consequently, a large library of amidinate ligands has become available [1][2][3][4][5][6][7][8][9].Closely related guanidinate anions can be accessed in a similarly manner by adding lithium diorganoamides, LiNR 2 , to carbodiimides.Making the amidinate and guanidinate ligands extremely versatile, the substituents at all three atoms of the N-C-N backbone can be varied.A generally applicable synthetic route to lithium amidinate precursors involves the addition of organolithium reagents to N,N′-disubstituted carbodiimides, as shown in Scheme 2. The substituents R and R′ can be varied in a wide range and, consequently, a large library of amidinate ligands has become available [1][2][3][4][5][6][7][8][9].Closely related guanidinate anions can be accessed in a similarly manner by adding lithium diorganoamides, LiNR2, to carbodiimides.At the outset of the present study, we wondered if it might be possible to directly attach a cyclopentadienyl ring to the amidinate N-C-N backbone by the use of sodium cyclopentadienide, NaCp, as a nucleophile.We now report the outcome of this reaction and the structural characterization of the unexpected product.

Results and Discussion
The reaction of 1 equiv. of sodium cyclopentadienide, NaCp, with N,N′-diisopropylcarbodiimide was carried out in THF solution at room temperature and resulted in formation of a clear, light-brown solution.Removal of the solvent, followed by extraction with n-pentane, provided a yellow solution besides a large amount of insoluble brown material.All attempts to crystallize the latter from diethyl ether or THF failed.Crystallization of the n-pentane filtrate at 4 °C afforded colorless, needle-like crystals in low yield.An IR spectrum of the product suggested that the expected simple addition reaction (Scheme 3a) had not taken place, as it showed three bands typical for NH functional groups at ν 3436 m (νas NH), 3386 m (νs NH), 3223 m (νs NH).A single-crystal X-ray diffraction study revealed the formation of an unexpected dimeric sodium half-sandwich complex [NaC5H3{C(NH i Pr)(=N i Pr)}2-1,2]2 (1).As illustrated in Scheme 3b, the bis(amidino)-substituted cyclopentadienyl anion [C5H3{C(NH i Pr)(=N i Pr)}2-1,2] − had formed through double addition of N,N′-diisopropylcarbodiimide to the cyclopentadienyl ring.With ca.9% (determined after the crystal structure had been elucidated) the isolated yield of 1 was reproducibly low, although synthetically useful amounts (>1 g) could be easily prepared.Notably and surprisingly, the isolated yield of 1 could not be improved by carrying out the reaction of NaCp with N,N′-diisopropylcarbodiimide in a 1:2 molar ratio as suggested by the composition of the products.Several experiments using 2 equiv. of i PrN=C=N i Pr under different reaction conditions afforded only small amounts of NaCp as the only crystalline material.At the outset of the present study, we wondered if it might be possible to directly attach a cyclopentadienyl ring to the amidinate N-C-N backbone by the use of sodium cyclopentadienide, NaCp, as a nucleophile.We now report the outcome of this reaction and the structural characterization of the unexpected product.

Results and Discussion
The reaction of 1 equiv. of sodium cyclopentadienide, NaCp, with N,N -diisopropylcarbodiimide was carried out in THF solution at room temperature and resulted in formation of a clear, light-brown solution.Removal of the solvent, followed by extraction with n-pentane, provided a yellow solution besides a large amount of insoluble brown material.All attempts to crystallize the latter from diethyl ether or THF failed.Crystallization of the n-pentane filtrate at 4 • C afforded colorless, needle-like crystals in low yield.An IR spectrum of the product suggested that the expected simple addition reaction (Scheme 3a) had not taken place, as it showed three bands typical for NH functional groups at ν 3436 m (ν as NH), 3386 m (ν s NH), 3223 m (ν s NH).A single-crystal X-ray diffraction study revealed the formation of an unexpected dimeric sodium half-sandwich complex [NaC 5 H 3 {C(NH i Pr)(=N i Pr)} 2 -1,2] 2 (1).As illustrated in Scheme 3b, the bis(amidino)-substituted cyclopentadienyl anion [C 5 H 3 {C(NH i Pr)(=N i Pr)} 2 -1,2] − had formed through double addition of N,N -diisopropylcarbodiimide to the cyclopentadienyl ring.With ca.9% (determined after the crystal structure had been elucidated) the isolated yield of 1 was reproducibly low, although synthetically useful amounts (>1 g) could be easily prepared.Notably and surprisingly, the isolated yield of 1 could not be improved by carrying out the reaction of NaCp with N,N -diisopropylcarbodiimide in a 1:2 molar ratio as suggested by the composition of the products.Several experiments using 2 equiv. of i PrN=C=N i Pr under different reaction conditions afforded only small amounts of NaCp as the only crystalline material.Colorless, needle-like single crystals of 1 suitable for X-ray diffraction were obtained by cooling a solution in n-pentane to 4 °C.Figure 1 depicts the molecular structures of 1 along with selected bond lengths and angles, while crystallographic details are listed in the Supplementary Materials.), which can be attributed to the higher coordination number of sodium in the reference compound [20].Consequently, it seems like the negative ligand charge is located at the amidine moiety at a significant amount.This is in accordance with amidinocyclopentadienide/aminofulvene-aldiminate mesomerism, as outlined in Scheme 4.  6) pm [22]).Coordination of further ligands, such as THF to sodium, is most likely prevented by the steric bulk of the isopropyl groups.Possibly for the same reason, the N-H hydrogen atoms at N2 and N4 are not involved in hydrogen bonding.Colorless, needle-like single crystals of 1 suitable for X-ray diffraction were obtained by cooling a solution in n-pentane to 4 • C. Figure 1  ), which can be attributed to the higher coordination number of sodium in the reference compound [20].Consequently, it seems like the negative ligand charge is located at the amidine moiety at a significant amount.This is in accordance with amidinocyclopentadienide/aminofulvene-aldiminate mesomerism, as outlined in Scheme 4. Colorless, needle-like single crystals of 1 suitable for X-ray diffraction were obtained by cooling a solution in n-pentane to 4 °C.Figure 1 depicts the molecular structures of 1 along with selected bond lengths and angles, while crystallographic details are listed in the Supplementary Materials.), which can be attributed to the higher coordination number of sodium in the reference compound [20].Consequently, it seems like the negative ligand charge is located at the amidine moiety at a significant amount.This is in accordance with amidinocyclopentadienide/aminofulvene-aldiminate mesomerism, as outlined in Scheme 4.  6) pm [22]).Coordination of further ligands, such as THF to sodium, is most likely prevented by the steric bulk of the isopropyl groups.Possibly for the same reason, the N-H hydrogen atoms at N2 and N4 are not involved in hydrogen bonding.6) pm [22]).Coordination of further ligands, such as THF to sodium, is most likely prevented by the steric bulk of the isopropyl groups.Possibly for the same reason, the N-H hydrogen atoms at N2 and N4 are not involved in hydrogen bonding.In the crystal, the dimeric molecule of 1 possesses inversion symmetry with the center of inversion right between the two Na atoms.According to the 1 H and 13 C NMR data of 1, the dimeric structure found in the crystal structure is partly retained in solution.Both the cyclopentadienyl and isopropyl resonance could be assigned.However, the 1 H NMR signals are significantly broadened, and in both NMR spectra a doubling of all resonances is observed.This can be interpreted by the presence of a slow equilibrium between the dimer and a (presumably THF-d8-solvated) monomeric structure in THF-d8 solution.Copies of the spectra can be found in the Supplementary Material.
With its two amidinate substituents in 1,2-position on the cyclopentadienyl ring, the new ligand in 1 belongs to the group of cyclopentadienyl derivatives called 6-aminofulvene-2-aldiminate (AFA) ligands.The first neutral 6-aminofulvene-2-aldimine (AFAH) compound was first prepared by Hafner et al. in 1963 [23,24].6-Aminofulvene-2-aldiminate ligands are ambidentate monoanionic ligands comprising both cyclopentadienyl and diimine donors, as shown in Scheme 5.As a consequence of this resonance, a 6-aminofulvene-2-aldiminate ligand can coordinate to a metal atom in a chelating mode through the two imine nitrogen donors as a fulvenealdiminate (A) or in an η 5 -mode as a cyclopentadienyldiimine. Complexes of this ligand system have been reported for some main group metals, as well as first and second row transition metals [25][26][27][28][29][30][31][32].Closer investigation of the coordination chemistry of 6-aminofulvene-2-aldiminate ligands began in 1998 with the discovery of a straightforward synthesis of the C-phenyl-substituted precursor C5H3[1,2-C(Ph)NH]2H based on the reaction of magnesocene with benzonitrile.The ligand C5H3[1,2-C(Ph)NH]2H was successfully employed in a number of complexes with Mg [25], Al, Ga [26] and Zr [25].In all these compounds, the 6-aminofulvene-2-aldiminate anion acts as a In the crystal, the dimeric molecule of 1 possesses inversion symmetry with the center of inversion right between the two Na atoms.According to the 1 H and 13 C NMR data of 1, the dimeric structure found in the crystal structure is partly retained in solution.Both the cyclopentadienyl and isopropyl resonance could be assigned.However, the 1 H NMR signals are significantly broadened, and in both NMR spectra a doubling of all resonances is observed.This can be interpreted by the presence of a slow equilibrium between the dimer and a (presumably THF-d 8 -solvated) monomeric structure in THF-d 8 solution.Copies of the spectra can be found in the Supplementary Material.
With its two amidinate substituents in 1,2-position on the cyclopentadienyl ring, the new ligand in 1 belongs to the group of cyclopentadienyl derivatives called 6-aminofulvene-2-aldiminate (AFA) ligands.The first neutral 6-aminofulvene-2-aldimine (AFAH) compound was first prepared by Hafner et al. in 1963 [23,24].6-Aminofulvene-2-aldiminate ligands are ambidentate monoanionic ligands comprising both cyclopentadienyl and diimine donors, as shown in Scheme 5.In the crystal, the dimeric molecule of 1 possesses inversion symmetry with the center of inversion right between the two Na atoms.According to the 1 H and 13 C NMR data of 1, the dimeric structure found in the crystal structure is partly retained in solution.Both the cyclopentadienyl and isopropyl resonance could be assigned.However, the 1 H NMR signals are significantly broadened, and in both NMR spectra a doubling of all resonances is observed.This can be interpreted by the presence of a slow equilibrium between the dimer and a (presumably THF-d8-solvated) monomeric structure in THF-d8 solution.Copies of the spectra can be found in the Supplementary Material.
With its two amidinate substituents in 1,2-position on the cyclopentadienyl ring, the new ligand in 1 belongs to the group of cyclopentadienyl derivatives called 6-aminofulvene-2-aldiminate (AFA) ligands.The first neutral 6-aminofulvene-2-aldimine (AFAH) compound was first prepared by Hafner et al. in 1963 [23,24].6-Aminofulvene-2-aldiminate ligands are ambidentate monoanionic ligands comprising both cyclopentadienyl and diimine donors, as shown in Scheme 5.As a consequence of this resonance, a 6-aminofulvene-2-aldiminate ligand can coordinate to a metal atom in a chelating mode through the two imine nitrogen donors as a fulvenealdiminate (A) or in an η 5 -mode as a cyclopentadienyldiimine. Complexes of this ligand system have been reported for some main group metals, as well as first and second row transition metals [25][26][27][28][29][30][31][32].Closer investigation of the coordination chemistry of 6-aminofulvene-2-aldiminate ligands began in 1998 with the discovery of a straightforward synthesis of the C-phenyl-substituted precursor C5H3[1,2-C(Ph)NH]2H based on the reaction of magnesocene with benzonitrile.The ligand C5H3[1,2-C(Ph)NH]2H was successfully employed in a number of complexes with Mg [25], Al, Ga [26] and Zr [25].In all these compounds, the 6-aminofulvene-2-aldiminate anion acts as a As a consequence of this resonance, a 6-aminofulvene-2-aldiminate ligand can coordinate to a metal atom in a chelating mode through the two imine nitrogen donors as a fulvenealdiminate (A) or in an η 5 -mode as a cyclopentadienyldiimine. Complexes of this ligand system have been reported for some main group metals, as well as first and second row transition metals [25][26][27][28][29][30][31][32].Closer investigation of the coordination chemistry of 6-aminofulvene-2-aldiminate ligands began in 1998 with the discovery of a straightforward synthesis of the C-phenyl-substituted precursor C 5 H 3 [1,2-C(Ph)NH] 2 H based on the reaction of magnesocene with benzonitrile.The ligand C 5 H 3 [1,2-C(Ph)NH] 2 H was successfully employed in a number of complexes with Mg [25], Al, Ga [26] and Zr [25].In all these compounds, the 6-aminofulvene-2-aldiminate anion acts as a N,N -chelating ligand.The same coordination mode was established for some 6-aminofulvene-2-aldiminate complexes of palladium [27,28], copper [29,30] and zinc [27], while the η 5 -coordination mode as a cyclopentadienyldiimine has been found in some AFA complexes of ruthenium [27,31].Notably, two magnesium complexes of the AFA ligand system bearing cyclohexyl groups at the nitrogen atoms have been reported, in which both coordination modes have been realized [32].Deprotonation of N,N -dicyclohexyl-6-aminofulvene-2-aldimine (HCy 2 AFA) with MeLi followed by reaction with MeMgBr afforded the N,N -coordinated complex [[1,2-(CyN=CH) 2 C 5 H 3 -N,N ]MgMe(THF)] with an uncoordinated cyclopentadienyl ring.In contrast, the direct reaction of HCy 2 AFA with MeMgBr resulted in liberation of methane and formation of the binuclear bromide-bridged complex Mg 2 (µ-Br)[µ-η 5 :κN,κN -1,2-(CyN=CH) 2 C 5 H 3 ][1,2-(CyN=CH) 2 C 5 H 3 -κN,κN ] in which one of the Mg centers is ligated both to the η 5 -cyclopentadienyl ring of one of the ligands and to both N donor atoms of the other.Thus, this magnesium derivative is the closest structural relative of our sodium complex 1, although the ligand system in 1 is rather unusual, as it bears additional secondary amino functionalities attached to the imine carbon atoms.It should be noted that the 1:1 addition of N-heterocyclic carbenes (NHCs) to carbodiimides has been reported.These reactions proceed in an analogous manner as outlined in Scheme 3a and afford zwitterionic neutral amidinate derivatives.The resulting imidazolium-2-amidinates have also been to be promising ligands in coordination chemistry [33][34][35].
When repeating the synthesis of 1, occasionally small amounts of block-like crystals of a second product first came out upon cooling of the n-pentane extract.These were characterized through their IR spectrum as well as single-crystal X-ray diffraction.The IR spectrum showed a characteristic ν C=O band at 1674 cm −1 , indicating the formation of a hydrolysis product.This was confirmed by the X-ray crystal structure determination, which revealed the presence of the dinuclear product {µ- (2), as shown in Scheme 6.The complex contains two formula moieties of N,N -diisopropylurea, which is the common hydrolysis product of N,N -diisopropylcarbodiimide.Even though the crystals of 2 did not allow for full structure refinement, the interatomic connectivity was clearly accessible.Just as in 1, the [C 5 H 3 {C(NH i Pr)(=N i Pr)} 2 -1,2] − ligand is attached to the Na atom in a N,N -chelating mode, but the cyclopentadiene moiety does not contribute to metal coordination.Consequently, in 2, the ligand can be regarded exclusively as an aminofulvene-aldiminate anion, as illustrated in the middle and the right formula in Scheme 4. Coordinative saturation of sodium is achieved by N,O-bridging coordination of two symmetry-equivalent ( i PrNH) 2 C=O moieties, resulting in a distorted tetrahedral environment of the metal atom.The bridging coordination mode of the N,N -diisopropylurea ligand leads to a dimeric structure with a centrosymmetric Na 2 O 2 C 2 N 2 eight-membered ring as the central motif.
Inorganics 2018, 6, x FOR PEER REVIEW 5 of 9 N,N′-chelating ligand.The same coordination mode was established for some 6-aminofulvene-2-aldiminate complexes of palladium [27,28], copper [29,30] and zinc [27], while the η 5 -coordination mode as a cyclopentadienyldiimine has been found in some AFA complexes of ruthenium [27,31].Notably, two magnesium complexes of the AFA ligand system bearing cyclohexyl groups at the nitrogen atoms have been reported, in which both coordination modes have been realized [32].Deprotonation of N,N′-dicyclohexyl-6-aminofulvene-2-aldimine (HCy2AFA  5 -cyclopentadienyl ring of one of the ligands and to both N donor atoms of the other.Thus, this magnesium derivative is the closest structural relative of our sodium complex 1, although the ligand system in 1 is rather unusual, as it bears additional secondary amino functionalities attached to the imine carbon atoms.It should be noted that the 1:1 addition of N-heterocyclic carbenes (NHCs) to carbodiimides has been reported.These reactions proceed in an analogous manner as outlined in Scheme 3a and afford zwitterionic neutral amidinate derivatives.The resulting imidazolium-2-amidinates have also been shown to be promising ligands in coordination chemistry [33][34][35].
When repeating the synthesis of 1, occasionally small amounts of block-like crystals of a second product first came out upon cooling of the n-pentane extract.These were characterized through their IR spectrum as well as single-crystal X-ray diffraction.The IR spectrum showed a characteristic ν C=O band at 1674 cm −1 , indicating the formation of a hydrolysis product.This was confirmed by the X-ray crystal structure determination, which revealed the presence of the dinuclear product {µ-( i PrNH)2C=O}2[NaC5H3{C(NH i Pr)(=N i Pr)}2-1,2]2 (2), as shown in Scheme 6.The complex contains two formula moieties of N,N′-diisopropylurea, which is the common hydrolysis product of N,N′-diisopropylcarbodiimide.Even though the crystals of 2 did not allow for full structure refinement, the interatomic connectivity was clearly accessible.Just as in 1, the [C5H3{C(NH i Pr)(=N i Pr)}2-1,2] − ligand is attached to the Na atom in a N,N′-chelating mode, but the cyclopentadiene moiety does not contribute to metal coordination.Consequently, in 2, the ligand can be regarded exclusively as an aminofulvene-aldiminate anion, as illustrated in the middle and the right formula in Scheme 4. Coordinative saturation of sodium is achieved by N,O-bridging coordination of two symmetry-equivalent ( i PrNH)2C=O moieties, resulting in a distorted tetrahedral environment of the metal atom.The bridging coordination mode of the N,N′-diisopropylurea ligand leads to a dimeric structure with a centrosymmetric Na2O2C2N2 eight-membered ring as the central motif.

Conclusions
The reaction of NaCp with N,N -diisopropylcarbodiimide did not result in formation of the expected sodium amidinate with a cyclopentadienyl ring attached to the central carbon atom of the amidinate backbone.Instead, the newly formed ligand [C 5 H 3 {C(NH i Pr)(=N i Pr)} 2 -1,2] − belongs to the group of ambidentate 6-aminofulvene-2-aldiminate ligands, which can coordinate to metal atoms either as N,N -fulvenealdiminates or in an η 5 -coordination mode as a cyclopentadienyldiimine.However, the anion [C 5 H 3 {C(NH i Pr)(=N i Pr)} 2 -1,2] − differs from all previously reported 6-aminofulvene-2-aldiminates in that the two substituents in 1,2-positions comprise additional secondary amino functionalities, providing another potential donor moiety.

General Procedures
All reactions were carried out in oven-dried or flame-dried glassware under an inert atmosphere of dry argon, employing standard Schlenk and glovebox techniques.The solvent THF was distilled from sodium/benzophenone under nitrogen atmosphere prior to use.Sodium cyclopentadienide (NaCp) was prepared according to the published method [36].N,N -Diisopropylcarbodiimide was purchased from Sigma-Aldrich (Steinheim, Germany) and used as received. 1H NMR (400 MHz) and 13 C NMR (100.6 MHz) spectra were recorded in THF-d 8 or toluene-d 8 solution on a Bruker DPX 400 spectrometer (Bruker BioSpin, Rheinstetten, Germany) at 25 • C. IR spectra were measured with a Bruker Vertex 70V spectrometer (Bruker Optics, Rheinstetten, Germany) equipped with a diamond ATR unit between 4000 cm −1 and 400 cm −1 .Microanalyses (C, H, N) were performed using a LECO CHNS 932 apparatus (LECO Corporation, Saint Joseph, MI, USA).In a 250 mL Schlenk flask, sodium cyclopentadienide (3.02 g, 34.4 mmol) was dissolved in THF (40 mL) and N,N -diisopropylcarbodiimide (4.37 g, 34.4 mmol) was added to the light-brown solution at r.t.while stirring.After stirring at r.t. for 48 h, the THF was removed in vacuo and the solid residue extracted with n-pentane (40 mL).A large amount of amorphous brown solid was separated by filtration and the clear yellow filtrate was concentrated in vacuo to ca. 20 mL.Cooling to 4 • C for a few days afforded colorless, needle-like crystals which were suitable for X-ray diffraction.Yield: 1.05 g (9%).Elemental analysis calcd.for C 38 H 66 N 8 Na 2 (680.98 g•mol −1 ): C, 67.02%; H, 9.77%; N, 16.45%; found C, 66.25%; H, 9.87%; N, 16.11%.Occasionally, when repeating the synthesis of 1, small amounts of block-like crystals of the hydrolysis product 2 first came out upon cooling of the n-pentane extract.These were characterized through their IR spectrum, as well as single-crystal X-ray diffraction.
Compound 1 crystallizes in the monoclinic space group P21/n, with one Na atom and one [C5H3{C(NH i Pr)(=N i Pr)}2-1,2] − ligand in the asymmetric unit.The dimeric molecular structure is completed by inversion symmetry.The ligand in attached to the Na atom in N,N-chelating fashion via the two non-protonated N atoms (N1, N3), with the bite angle N-Na-N being 91.03(5)°.The two Na-N bonds are virtually identical in length (Na-N1 233.1(2) pm and Na-N3 233.8(2) pm).These values are slightly smaller as compared to those in a previously reported sodium amidinate (Na-N 237.1(3) and 240.7(3) pm; C.N. of Na = 5
depicts the molecular structures of 1 along with selected bond lengths and angles, while crystallographic details are listed in the Supplementary Materials.Compound 1 crystallizes in the monoclinic space group P2 1 /n, with one Na atom and one [C 5 H 3 {C(NH i Pr)(=N i Pr)} 2 -1,2] − ligand in the asymmetric unit.The dimeric molecular structure is completed by inversion symmetry.The ligand in attached to the Na atom in N,N-chelating fashion via the two non-protonated N atoms (N1, N3), with the bite angle N-Na-N being 91.03(5) • .The two Na-N bonds are virtually identical in length (Na-N1 233.1(2) pm and Na-N3 233.8(2) pm).These values are slightly smaller as compared to those in a previously reported sodium amidinate (Na-N 237.1(3) and 240.7(3) pm; C.N. of Na = 5
Compound 1 crystallizes in the monoclinic space group P21/n, with one Na atom and one [C5H3{C(NH i Pr)(=N i Pr)}2-1,2] − ligand in the asymmetric unit.The dimeric molecular structure is completed by inversion symmetry.The ligand in attached to the Na atom in N,N-chelating fashion via the two non-protonated N atoms (N1, N3), with the bite angle N-Na-N being 91.03(5)°.The two Na-N bonds are virtually identical in length (Na-N1 233.1(2) pm and Na-N3 233.8(2) pm).These values are slightly smaller as compared to those in a previously reported sodium amidinate (Na-N 237.1(3) and 240.7(3) pm; C.N. of Na = 5
13 C