Triphenylcyanoborate Complexes of Rhodium. A Nitrogen-15 NMR Study of [Rh(NCBPh₃)(PPh₃)₃] and [Rh(CNBPh₃)(PPh₃)₃] and Their Derivatives

Abstract

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.

Structural evolution of a recoverable rhodium hydrogenation catalyst

“…This is consistent with the formation of a Rh-N bond, based on the chemical shifts for other Rh-N compounds [23,24] and provides the first direct spectroscopic evidence of Rh-glycine attachment through the amine [25][26][27][28]. The observed linewidth of 45 Hz eliminated the possibility of observing the Rh-N coupling, typically on the order of 5-20 Hz [23]. To confirm that the binding was through the amine and not through the acid group of glycine, the experiment was repeated with FMOC (fluorenylmethoxycarbonyl)-protected glycine (FMOC-15 NH-CH 2 -COOH).…”

Interaction of Triphenyltin Hydride and Rhodium. Structure of [Rh(NCBPh3)(H)(SnPh3)(PPh3)2] and NMR (1H,15N,31P,103Rh,119Sn) Study of Pyridine-Containing Derivatives

“…Thermal Stability of 1 and 6. On gentle heating (≥35 °C) in dichloromethane or toluene, 6 , prepared in situ from 1 and L, undergoes reductive elimination of Ph 3 SnH to give, in the presence of free PPh 3 released by 1 in the reaction with L, cis -[Rh(NCBPh 3 )(PPh 3 ) 2 (L)] (this compound is reported in ref ), as shown by the 31 P{ 1 H} spectrum in Figure a,b. The low solubility of both 1 and 4-Me 2 Npy in toluene necessitates the use of dichloromethane or dichloromethane/toluene mixtures.…”

“…With pyridine and substituted pyridines in dichloromethane or toluene at −25 °C, 1 reacts to give a colorless solution containing trans -[Rh(NCBPh 3 )(H)(SnPh 3 )(PPh 3 ) 2 (L)] ( 2a − c ) (L = ( a ) py, ( b ) 4-Me 2 Npy, ( c ) 4-MeO 2 Cpy) as the only product. The geometry is confirmed by (i) the 31 P{ 1 H} spectrum, which consists of a doublet with tin satellites (Figure a), (ii) the 1 H (Figure b,c) and 15 N{ 1 H} and 119 Sn{ 1 H} (Figure g) spectra in which the signals show coupling to two equivalent 31 P nuclei, and (iii) the magnitudes of J (Sn−P) and J (N−H) , (Table ), which are characteristic of cis and trans couplings, respectively. The binding of pyridine to the vacant site trans to tin causes a shift to high frequency of δ( 31 P) and δ( 103 Rh), a shift to low frequency of δ 1 H, δ( 15 N), and δ( 119 Sn) and an increase in J (Sn−H) by a factor greater than 4.…”

“…[Rh(NCBPh 3 )(H)(SnPh 3 )(PPh 3 ) 2 ], in both unenriched and 99% 15 N-enriched forms, was prepared by a method already reported …”

(PPh3)3RhCNB(CF3)3and (PPh3)3RhNCB(CF3)3: Isocyano- and Cyanoborate Complexes of Tris(triphenylphosphine)rhodium(I)

“…Since the discovery of Wilkinsons catalyst, chlorotris(triphenylphosphine)rhodium(I), (PPh 3 ) 3 RhCl, in 1964, numerous applications in catalytic processes have been developed such as hydrogenations and hydroformulations . Many derivatives of (PPh 3 ) 3 RhCl have been synthesized, and their chemistry has been investigated, especially their catalytic properties. , In addition, the chloro ligand was replaced by cyano, NCBPh 3 , CNBPh 3 , − NCMe, , and many other groups.…”