Bis(6-Diphenylphosphinoacenaphth-5-yl)Telluride as a Ligand toward Manganese and Rhenium Carbonyls

The reaction of the previously known bis(6-diphenylphosphinoacenaphthyl-5-)telluride (6-Ph2P-Ace-5-)2Te (IV) with (CO)5ReCl and (CO)5MnBr proceeded with the liberation of CO and provided fac-(6-Ph2P-Ace-5-)2TeM(X)(CO)3 (fac-1: M = Re, X = Cl; fac-2: M = Mn, X = Br), in which IV acts as bidentate ligand. In solution, fac-1 and fac-2 are engaged in a reversible equilibrium with mer-(6-Ph2P-Ace-5-)2TeM(X)(CO)3 (mer-1: M = Re, X = Cl; mer-2: M = Mn, X = Br). Unlike fac-1, fac-2 is prone to release another equivalent of CO to give (6-Ph2P-Ace-5-)2TeMn(Br)(CO)2 (3), in which IV serves as tridentate ligand.


Introduction
Transition metal complexes composed of multidentate ligands based upon tellurium are far less explored than those of sulfur and selenium, which might be due to the lack of easily available ligands containing tellurium, as well as the historical misconception that organotellurium compounds were extremely malodorous and toxic [1][2][3][4][5][6][7][8]. Up to the 1970s, studies of coordination chemistry were mostly restricted to monodentate ligands. The first bidentate telluroether ligand I (Te, P-type) was described by Gysling and Luss in 1984 [9], whereas the first tridentate telluroethers II (N,Te,N-type), and III (P,Te,P-type) were reported by Singh et al. [10] as well as Lin and Gabbaï (Scheme 1) [11].

Introduction
Transition metal complexes composed of multidentate ligands based upon tellurium are far less explored than those of sulfur and selenium, which might be due to the lack of easily available ligands containing tellurium, as well as the historical misconception that organotellurium compounds were extremely malodorous and toxic [1][2][3][4][5][6][7][8]. Up to the 1970s, studies of coordination chemistry were mostly restricted to monodentate ligands. The first bidentate telluroether ligand I (Te, P-type) was described by Gysling and Luss in 1984 [9], whereas the first tridentate telluroethers II (N,Te,N-type), and III (P,Te,P-type) were reported by Singh et al. [10] as well as Lin and Gabbaï (Scheme 1) [11]. In preceding work, we reported on the synthesis of bis(6-diphenylphosphinoacenaphth-5-yl) telluride (IV) [12], which also holds potential as a tridentate telluroether ligand. Herein, we describe the reaction of IV with (CO) 5 MnBr and (CO) 5 ReCl, giving rise to the formation of three octahedral transition metal carbonyl complexes with this ligand.
The analogous reaction of IV with (CO)5MnBr in THF at 65° occurred within 32 h and gave rise to the isomeric mixture of fac/mer-(6-Ph2P-Ace-5-)2TeMe(Br)(CO)3 (fac-2/mer-2) and as was already observed for the Te-Re complex fac-1, fac-2 precipitates solely from the reaction mixture upon cooling to r.t. and was isolated in 47% yield (Scheme 2). In both complexes fac-1 and fac-2, the telluroether IV serves as bidentate ligand. In the solid-state, fac-1 and fac-2 are reasonably stable toward moist air and show no signs of decomposition even after prolonged times of storage. Unfortunately, both complexes show only poor solubility in the most common solvents used for NMR spectroscopy. In CDCl3 solution, both fac-1 and fac-2 are in equilibrium with their related meridional complexes mer-1 and mer-2, which can be inferred by 31 P-NMR spectroscopy (Scheme 3). The 31 P-NMR spectrum of a freshly prepared solution of fac-1 in CDCl3, shows almost exclusively two chemical shifts at δ = −0.9 and −25.0 ppm of equal intensity, which are assigned to the P atom that coordinates to the Re atom and the P atom that engages in interaction with the Te atom (the assignment is based upon the comparison with fac-[Re(Cl)(CO)3(PPh2C10H6PPh2)] [13], ([(Ph2P(Me2pz)2)Re(CO)3Br] and [(Ph2P(Me2pz))Re(CO)4Br (pz = pyrazole) [14]). However, the formation of mer-1 can already be detected even from the freshly prepared solution of fac-1, showing chemical shifts at δ = 14.7 and −26.4 ppm, which increase in intensity over time ( Figure 1). It should be noted that the chemical shifts of fac-1 consist of singlets, whereas the doublets were observed for mer-1 with a coupling constant of J( 31 P-31 P) = 11.6 Hz. In contrast, the Te-Mn complex 2 shows significantly faster formation of mer-2 (δ ( 31 P) = 50.0 and −28.0 ppm) from a freshly prepared solution of fac-1 (δ ( 31 P) = 36.2 and −25.6 ppm, Figure S2d). The analogous reaction of IV with (CO) 5 MnBr in THF at 65 • occurred within 32 h and gave rise to the isomeric mixture of fac/mer-(6-Ph 2 P-Ace-5-) 2 TeMe(Br)(CO) 3 (fac-2/mer-2) and as was already observed for the Te-Re complex fac-1, fac-2 precipitates solely from the reaction mixture upon cooling to r.t. and was isolated in 47% yield (Scheme 2). In both complexes fac-1 and fac-2, the telluroether IV serves as bidentate ligand. In the solid-state, fac-1 and fac-2 are reasonably stable toward moist air and show no signs of decomposition even after prolonged times of storage. Unfortunately, both complexes show only poor solubility in the most common solvents used for NMR spectroscopy. In CDCl 3 solution, both fac-1 and fac-2 are in equilibrium with their related meridional complexes mer-1 and mer-2, which can be inferred by 31 P-NMR spectroscopy (Scheme 3). The 31 P-NMR spectrum of a freshly prepared solution of fac-1 in CDCl 3 , shows almost exclusively two chemical shifts at δ = −0.9 and −25.0 ppm of equal intensity, which are assigned to the P atom that coordinates to the Re atom and the P atom that engages in interaction with the Te atom (the assignment is based upon the comparison with fac-[Re(Cl)(CO) 3 (PPh 2 C 10 H 6 PPh 2 )] [13], ([(Ph 2 P(Me 2 pz) 2 )Re(CO) 3 Br] and [(Ph 2 P(Me 2 pz))Re(CO) 4 Br (pz = pyrazole) [14]). However, the formation of mer-1 can already be detected even from the freshly prepared solution of fac-1, showing chemical shifts at δ = 14.7 and −26.4 ppm, which increase in intensity over time ( Figure 1). It should be noted that the chemical shifts of fac-1 consist of singlets, whereas the doublets were observed for mer-1 with a coupling constant of J( 31 P-31 P) = 11.6 Hz. In contrast, the Te-Mn complex 2 shows significantly faster formation of mer-2 (δ ( 31 P) = 50.0 and −28.0 ppm) from a freshly prepared solution of fac-1 (δ ( 31 P) = 36.2 and −25.6 ppm, Figure S2d).  When the reaction of IV with (CO)5MnBr was repeated with a longer reaction time of 7 days, a different product, namely (6-Ph2P-Ace-5-)2TeMn(Br)(CO)2 (3) formed, which was obtained in 40% isolated yield (Scheme 2). The formation of 3 can be rationalized by the liberation of CO from fac-2 and/or mer-2. In 3, the telluroether serves as tridentate ligand. Notably, a similar reactivity of fac-1 was not observed. The solubility of 3 in the most common solvents is slightly higher than those of fac-1 and fac-2, which allowed the acquisition of full set of NMR data. The 31 P-NMR spectrum (CDCl3) of 3 shows a broad signal at δ = 59.7 ppm (ω1/2 = 110 Hz), whereas the 125 Te-NMR spectrum exhibits a singlet at δ = 753.1 pm that is slightly high-field shifted in comparison to IV (δ = 704.4 ppm) [12].
The   When the reaction of IV with (CO)5MnBr was repeated with a longer reaction time of 7 days, a different product, namely (6-Ph2P-Ace-5-)2TeMn(Br)(CO)2 (3) formed, which was obtained in 40% isolated yield (Scheme 2). The formation of 3 can be rationalized by the liberation of CO from fac-2 and/or mer-2. In 3, the telluroether serves as tridentate ligand. Notably, a similar reactivity of fac-1 was not observed. The solubility of 3 in the most common solvents is slightly higher than those of fac-1 and fac-2, which allowed the acquisition of full set of NMR data. The 31 P-NMR spectrum (CDCl3) of 3 shows a broad signal at δ = 59.7 ppm (ω1/2 = 110 Hz), whereas the 125 Te-NMR spectrum exhibits a singlet at δ = 753.1 pm that is slightly high-field shifted in comparison to IV (δ = 704.4 ppm) [12].
The  When the reaction of IV with (CO) 5 MnBr was repeated with a longer reaction time of 7 days, a different product, namely (6-Ph 2 P-Ace-5-) 2 TeMn(Br)(CO) 2 (3) formed, which was obtained in 40% isolated yield (Scheme 2). The formation of 3 can be rationalized by the liberation of CO from fac-2 and/or mer-2. In 3, the telluroether serves as tridentate ligand. Notably, a similar reactivity of fac-1 was not observed. The solubility of 3 in the most common solvents is slightly higher than those of fac-1 and fac-2, which allowed the acquisition of full set of NMR data. The 31 P-NMR spectrum (CDCl 3 ) of 3 shows a broad signal at δ = 59.7 ppm (ω 1/2 = 110 Hz), whereas the 125 Te-NMR spectrum exhibits a singlet at δ = 753.1 pm that is slightly high-field shifted in comparison to IV (δ = 704.4 ppm) [12].

Experimental Section
General. Reagents were obtained commercially (Sigma-Aldrich, Taufkirchen, Germany) and were used as received. Dry solvents were collected from an SPS800 mBraun solvent system. Bis(6-diphenylacenaphth-5-yl)telluride, (6-Ph 2 P-Ace-5-) 2 Te (IV) was prepared according to literature procedures [12]. 1 H-, 13 C-, 31 P-, and 125 Te-NMR spectra were recorded at room temperature using a Bruker Avance-360 and a Bruker Avance-200 spectrometer and are referenced to tetramethylsilane ( 1 H, 13 C), phosphoric acid (85% in water) ( 31 P), and dimethyltelluride ( 125 Te). Chemical shifts are reported in parts per million (ppm), and coupling constants (J) are given in Hertz (Hz). The FTIR spectra were recorded on Thermo Scientific Nicolet TM iS10. The ESI-MS spectra were obtained with a Bruker Esquire-LC MS. Dichloromethane/acetonitrile solutions (c = 1 × 10 −6 mol L −1 ) were injected directly into the spectrometer at a flow rate of 3 µL min −1 . Nitrogen was used both as a drying gas and for nebulization with flow rates of approximately 5 L min −1 and a pressure of 5 psi. Pressure in the mass analyzer region was usually about 1 × 10 −5 mbar. Spectra were collected for 1 min and averaged. The nozzle-skimmer voltage was adjusted individually for each measurement.

Supplementary Materials:
The following are available online.
Author Contributions: T.G.D. carried out the experimental work, the spectroscopic characterization and participated in writing the manuscript. As Co-Investor, E.H. was involved in the interpretation of the results and also participated in writing the manuscript. As Crystallographer, E.L. carried out the X-ray structure analyses. As Principal Investigator, J.B. was responsible for writing the publication.