The isomeric compounds [Rh(NCBPh 3 )(PPh 3 ) 3 ] (1) (prepared from [RhCl(PPh 3 ) 3 ] and K[NCBPh 3 ]) and )(PPh 3 ) 3 ] (2) (prepared from [Rh(CN)(PPh 3 ) 3 ] and BPh 3 ) undergo ligand exchange with pyridine (py) to give cis-[Rh(NCBPh 3 )(PPh 3 ) 2 (py)] and trans-[Rh(CNBPh 3 )(PPh 3 ) 2 (py)] and with L ) ethylene (reversibly), carbon monoxide, and 2,6-xylyl isocyanide (XNC) to give trans-[Rh(X)(PPh 3 ) 2 (L)] (X ) NCBPh 3 , CNBPh 3 ) and oxidative addition with hydrogen (reversibly) and triphenyltin hydride to give [Rh(X)(H) 2 (PPh 3 ) 3 ] and [Rh(X)(H)(SnPh 3 )-(PPh 3 ) 2 ], respectively; triphenylsilane combines with 1 (reversibly) but not with 2. By heating 1 to 100 °C in an inert solvent, the rearrangement of 1 to 2 is observed. Complex 1 in DMSO combines with oxygen to yield a product formulated as a sulfonium salt, although in CH 2 Cl 2 it is unreactive toward oxygen unlike 2 which forms an O 2 adduct. In a solution of toluene containing pyridine or substituted pyridines in the presence of oxygen, 1 forms cis-[Rh(NCBPh 3 )(O 2 )(PPh 3 ) 2 (py)] while 2 loses BPh 3 to give [Rh(CN)(O 2 )(PPh 3 ) 2 (py)]. Hydrogen is bound reversibly by trans-[Rh(CNBPh 3 )(PPh 3 ) 2 (py)] and irreversibly by cis-[Rh(NCBPh 3 )(PPh 3 ) 2 (py)]. A comparison of the properties of 1 and 2 and their derivatives shows the N-bonded isomers to be the more electrophilic and the N-B bond to be significantly more labile than the C-B bond. Nitrogen-15 NMR data are reported for complexes enriched to 99% in 15 N.
The structure of [Rh(NCBPh(3))(H)(SnPh(3))(PPh(3))(2)] (1) (formed from [Rh(NCBPh(3))(PPh(3))(3)] and Ph(3)SnH) was determined by a single-crystal X-ray diffraction study which shows the geometry to be equally well described as a distorted tetragonal pyramid with tin at the apex or a distorted trigonal bipyramid with a hydrogen of one of the phosphine phenyl groups occupying the sixth coordination site. The tin-hydride distance of 2.31(5) Å is consistent with a weak interaction. Crystal data for 1: space group, P2(1)/c; a = 12.564(4), b = 26.942(4), c = 18.000(3) Å; beta = 92.93(2) degrees; V = 6085(2) Å(3); Z = 4; R = 0.050 for 5655 reflections with I >/= 2sigma(I). Complex 1 reacts with pyridine and substituted pyridines L (L = pyridine (py) (a), 4-(dimethylamino)pyridine (4-Me(2)Npy) (b), and 4-carbomethoxypyridine (4-MeO(2)Cpy) (c)) in dichloromethane at -25 degrees C to give trans-[Rh(NCBPh(3))(H)(SnPh(3))(PPh(3))(2)(L)] (2a-c). With L = 4-Me(2)Npy, the products cis-[Rh(NCBPh(3))(H)(SnPh(3))(PPh(3))(2)(4-Me(2)Npy)] (3) and cis- and trans-[Rh(NCBPh(3))(H)(SnPh(3))(PPh(3))(4-Me(2)Npy)(2)] (4 and 5, respectively) are also formed. At room temperature, [Rh(NCBPh(3))(H)(SnPh(3))(PPh(3))(L)] (6a-c) is the final product, decomposing over a period of hours. The pyridine-containing complexes were not isolated and were characterized by NMR spectroscopy, which showed the magnitude of the spin coupling constant J(Sn-H) to increase by factors of up to 5.5 compared with the value of 29 Hz observed for 1. At 50 degrees C, 6 (in the presence of L and PPh(3) originating from 1) undergoes reductive elimination of Ph(3)SnH to give cis-[Rh(NCBPh(3))(PPh(3))(2)(L)]; at this temperature 1 is stable, decomposing only at temperatures of 85 degrees C and above. A kinetic study of the dissociation of Ph(3)SnH from 6b (L = 4-Me(2)Npy) gave activation parameters DeltaH() = 97 +/- 6 kJ mol(-)(1) and DeltaS() = 1 +/- 20 J K(-)(1) mol(-)(1). The weakened interaction between Ph(3)SnH and rhodium is accounted for in terms of a three-center "agostic" bond.
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