P-fluorous Phosphines as Electron-poor/fluorous Hybrid Functional Ligands for Precious Metal Catalysts: Synthesis of Rh(i), Ir(i), Pt(ii), and Au(i) Complexes Bearing P-fluorous Phosphine Ligands

P-Fluorous phosphine (R 2 PR f), in which the perfluoroalkyl group is directly bonded to the phosphorus atom, is a promising ligand because it has a hybrid functionality, i.e., electron-poor and fluorous ligands. However, examples of P-fluorous phosphine–metal complexes are still rare, most probably because the P-fluorous group is believed to decrease the coordination ability of the phosphines dramatically. In contrast, however, we have succeeded in synthesizing a series of P-fluorous phosphine–coordinated metal complexes such as rhodium, iridium, platinum, and gold. Furthermore, the electronic properties of R 2


Introduction
P-Fluorous phosphine (R 2 PR f ), in which the perfluoroalkyl group is directly bonded to the phosphorus atom, is a hybrid functional phosphine ligand having both "electron-poor" [1] and "fluorous" [2][3][4][5][6][7][8] characteristics.Since strongly electron-withdrawing ligands are known to promote reductive elimination steps in catalytic reactions, the former property may be exploited, not only to optimize known reactions, but also to develop new catalytic reactions [9][10][11][12].As to the latter property, the use of a fluorous biphasic system (FBS) may make it possible to recover catalysts and ligands easily and to reuse them for catalytic reactions.We recently developed a catalytic reaction using P-fluorous phosphines as ligands, i.e., a palladium-catalyzed cross-coupling reaction between acid chlorides and terminal alkynes, and have demonstrated the recyclability of the catalyst and the ligand [13].Namely, the poor electron density of the P-fluorous phosphine ligands induced the palladium-catalyzed cross-coupling reaction, even under copper-free conditions, and the fluorous affinity of P-fluorous phosphines enabled the reuse of their Pd-complexes by using an FBS.
Our group recently developed three types of convenient synthetic methods of P-fluorous phosphine ligands (R 2 PR f ) (see, Scheme 1): method A, the photoinduced direct displacement of R 3 P with R f I under radical conditions [13]; method B, the photoinduced S H 2 reaction of (Ph 2 P) 2 with R f I [14]; method C, the reductive substitution reaction of diphenyl(2,4,6-trimethylbenzoyl)phosphine oxide (TMDPO, known as a representative radical initiator for polymerization) with R f I under light [15].
Our group recently developed three types of convenient synthetic methods of P-fluorous phosphine ligands (R2PRf) (see, Scheme 1): method A, the photoinduced direct displacement of R3P with RfI under radical conditions [13]; method B, the photoinduced SH2 reaction of (Ph2P)2 with RfI [14]; method C, the reductive substitution reaction of diphenyl(2,4,6-trimethylbenzoyl)phosphine oxide (TMDPO, known as a representative radical initiator for polymerization) with RfI under light [15].To synthesize a diphenyl-substituted P-fluorous phosphine ligand (Ph2P n C10F21 1a), method C is the best because method C can be applied to the gram-scale synthesis of 1a (Equation ( 1)) [15].In the case of the synthesis of the dialkyl-substituted P-fluorous phosphine ligand ( n Bu2P n C10F21 1b), method A is the most suitable because the gram scale of 1b can be obtained by this method (Equation (2)).
(1) (2) Our recent success in palladium-catalyzed cross-coupling using P-fluorous phosphines [13] and the establishment of their synthetic methods [13][14][15] strongly suggest their promising usability as functional ligands in many transition metal-catalyzed reactions.However, examples of P-fluorous phosphine-metal complexes are still rare in the literature [16][17][18][19][20], and are limited to metal-R2PRf complexes bearing a short-chain perfluoroalkyl (light fluorous) group, which cannot be separated by a FBS due to the low content of fluorine atoms.To encourage the use of P-fluorous phosphine ligands in various catalytic reactions, we investigated their reactions with representative transition metal catalysts to prepare the corresponding P-fluorous phosphine-coordinated metal catalysts.In this paper, we report the synthesis of P-fluorous phosphine-coordinated rhodium, iridium, platinum, and gold complexes, and also describe their electronic properties, structural features, and catalytic activities.To synthesize a diphenyl-substituted P-fluorous phosphine ligand (Ph 2 P n C 10 F 21 1a), method C is the best because method C can be applied to the gram-scale synthesis of 1a (Equation ( 1)) [15].In the case of the synthesis of the dialkyl-substituted P-fluorous phosphine ligand ( n Bu 2 P n C 10 F 21 1b), method A is the most suitable because the gram scale of 1b can be obtained by this method (Equation ( 2)).

Results and Discussion
Our group recently developed three types of convenient synthetic methods of P-fluorous phosphine ligands (R2PRf) (see, Scheme 1): method A, the photoinduced direct displacement of R3P with RfI under radical conditions [13]; method B, the photoinduced SH2 reaction of (Ph2P)2 with RfI [14]; method C, the reductive substitution reaction of diphenyl(2,4,6-trimethylbenzoyl)phosphine oxide (TMDPO, known as a representative radical initiator for polymerization) with RfI under light [15].To synthesize a diphenyl-substituted P-fluorous phosphine ligand (Ph2P n C10F21 1a), method C is the best because method C can be applied to the gram-scale synthesis of 1a (Equation ( 1)) [15].In the case of the synthesis of the dialkyl-substituted P-fluorous phosphine ligand ( n Bu2P n C10F21 1b), method A is the most suitable because the gram scale of 1b can be obtained by this method (Equation (2)). (1) (2) Our recent success in palladium-catalyzed cross-coupling using P-fluorous phosphines [13] and the establishment of their synthetic methods [13-15] strongly suggest their promising usability as functional ligands in many transition metal-catalyzed reactions.However, examples of P-fluorous phosphine-metal complexes are still rare in the literature [16][17][18][19][20], and are limited to metal-R2PRf complexes bearing a short-chain perfluoroalkyl (light fluorous) group, which cannot be separated by a FBS due to the low content of fluorine atoms.To encourage the use of P-fluorous phosphine ligands in various catalytic reactions, we investigated their reactions with representative transition metal catalysts to prepare the corresponding P-fluorous phosphine-coordinated metal catalysts.In this paper, we report the synthesis of P-fluorous phosphine-coordinated rhodium, iridium, platinum, and gold complexes, and also describe their electronic properties, structural features, and catalytic activities.Our group recently developed three types of convenient synthetic methods of P-fluorous phosphine ligands (R2PRf) (see, Scheme 1): method A, the photoinduced direct displacement of R3P with RfI under radical conditions [13]; method B, the photoinduced SH2 reaction of (Ph2P)2 with RfI [14]; method C, the reductive substitution reaction of diphenyl(2,4,6-trimethylbenzoyl)phosphine oxide (TMDPO, known as a representative radical initiator for polymerization) with RfI under light [15].To synthesize a diphenyl-substituted P-fluorous phosphine ligand (Ph2P n C10F21 1a), method C is the best because method C can be applied to the gram-scale synthesis of 1a (Equation ( 1)) [15].In the case of the synthesis of the dialkyl-substituted P-fluorous phosphine ligand ( n Bu2P n C10F21 1b), method A is the most suitable because the gram scale of 1b can be obtained by this method (Equation (2)).

Results and Discussion
(1) (2) Our recent success in palladium-catalyzed cross-coupling using P-fluorous phosphines [13] and the establishment of their synthetic methods [13-15] strongly suggest their promising usability as functional ligands in many transition metal-catalyzed reactions.However, examples of P-fluorous phosphine-metal complexes are still rare in the literature [16][17][18][19][20], and are limited to metal-R2PRf complexes bearing a short-chain perfluoroalkyl (light fluorous) group, which cannot be separated by a FBS due to the low content of fluorine atoms.To encourage the use of P-fluorous phosphine ligands in various catalytic reactions, we investigated their reactions with representative transition metal catalysts to prepare the corresponding P-fluorous phosphine-coordinated metal catalysts.In this paper, we report the synthesis of P-fluorous phosphine-coordinated rhodium, iridium, platinum, and gold complexes, and also describe their electronic properties, structural features, and catalytic activities.

Results and Discussion
(2) Our recent success in palladium-catalyzed cross-coupling using P-fluorous phosphines [13] and the establishment of their synthetic methods [13-15] strongly suggest their promising usability as functional ligands in many transition metal-catalyzed reactions.However, examples of P-fluorous phosphine-metal complexes are still rare in the literature [16][17][18][19][20], and are limited to metal-R 2 PR f complexes bearing a short-chain perfluoroalkyl (light fluorous) group, which cannot be separated by a FBS due to the low content of fluorine atoms.To encourage the use of P-fluorous phosphine ligands in various catalytic reactions, we investigated their reactions with representative transition metal catalysts to prepare the corresponding P-fluorous phosphine-coordinated metal catalysts.In this paper, we report the synthesis of P-fluorous phosphine-coordinated rhodium, iridium, platinum, and gold complexes, and also describe their electronic properties, structural features, and catalytic activities.

Results and Discussion
First, we investigated the coordination of R 2 PR f to Pt.When a mixture of Ph 2 P n C 10 F 21 (1a) and PtCl 2 (CH 3 CN) 2 was stirred in CHCl 3 for two days, the P-perfluoroalkylated phosphine-platinum complex, PtCl 2 (Ph 2 P n C 10 F 21 ) 2 (2a), was obtained successfully (Equation (3)).The 31 P NMR spectrum showed a triplet with satellites (J P-F = 55.8Hz, J P-Pt = 3878 Hz).This indicated the successful complexation between the P-fluorous phosphine-platinum complex.When n Bu 2 P n C 10 F 21 (1b) was used, instead of 1a, for complexation with platinum under similar conditions, the P-perfluoroalkylated phosphine-platinum complex trans-PtCl 2 ( n Bu 2 P n C 10 F 21 ) 2 (2b) was also obtained in good yield (Equation ( 3)).

General Comments
Ph 2 P n C 10 F 21 (1a) [15] and n Bu 2 P n C 10 F 21 (1b) [13] were synthesized according to the literature.Other materials were obtained from commercial suppliers and used without purification before use.
F NMR and 31 P NMR analyses confirmed the complexation of 1a with gold(I).The 19 F NMR signal of P-CF 2 -CF 2appeared at −107.8 ppm (CDCl 3 ) as a doublet of triplets ( 2 J F-P = 64.1 Hz, 3 J F-F = 14.2 Hz), which was shifted downfield to 0.9 ppm compared with the free P-CF 2 -CF 2 -of Ph 2 P n C 10 F 21 , due to metal complexation.The 31 P NMR signal appeared at 40.1 ppm as a triplet of triplets ( 2 J P-F = 65.0Hz, 3 J P-F = 12.9 Hz) in CH 2 Cl 2 .HRMS (FAB) analysis further confirmed the complexation: the found value 900.9848 (calculated value for C 22 H 10 F 21 PAu [M − Cl] + : 900.9850) indicated the presence of the Au(Ph 2 P n C 10 F 21 ) moiety.Inorganics 2017, 5, 5 5 of 10 [27], as well as that of the rhodium complex.The symmetry of the 31 P NMR spectrum (δP 45.0 ppm, t, JP-F = 34.6Hz) indicates that the steric configuration of 4a is trans.