Rh(I) carbonyl carboxylato complexes: Spectral and structural characteristics. Some reactions of coordinated formate group

Abstract

Dirhodium(I) di( µ -carboxylato) tetracarbonyls[ Rh ( µ -RCOO )( CO ) 2 ] 2 were obtained for the first time by reacting rhodium(I) carbonyl chloride dimer [ Rh ( µ -Cl )( CO ) 2 ] 2 with silver carboxylates [1]. The authors [1] synthesized and characterized acetate, trifluoroacetate, p -fluorobenzoate, and phthalate complexes of this type and some bis(phosphine) derivatives, such as transRh ( RCOO )( PPh 3 ) 2 ( CO ) . Later, some other methods were developed for synthesizing [ Rh ( µ -RCOO )( CO ) 2 ] 2 complexes with R = CH 3 ( II ), CF 3 ( III ) [2-4] and their monocarbonyl triphenylphosphine derivatives transRh ( RCOO )( PPh 3 ) 2 ( CO ) [2,[5][6][7][8][9][10][11][12]. The authors of [4] reported the results of X-ray diffraction study of [ Rh ( µ -The structure of transRh ( CF 3 COO )( PPh 3 ) 2 ( CO ) was previously determined in [13].Rhodium(I) formate complexes became available considerably later. Thus, the carbonyl formate dimer [ Rh ( µ -HCOO )( CO ) 2 ] 2 ( I ) was synthesized for the first time via a reaction of dirhodium(II) tetraacetate with carbon monoxide in formic acid [14]. Some other methods of synthesis of this compound were reported later on in [15,16]. A series of bis(phosphine) complexes trans -Rh ( HCOO )( PR 3 ) 2 ( CO ) was also synthesized [17][18][19]. The molecular structure of transRh ( HCOO )( PPh 3 ) 2 ( CO ) ( IV ) was determined by X-ray diffraction method [17]. It should be noted that in subsequent years, rhodium(I) formate complexes with carbonyl and some other π -acceptor ligands (olefins, phosphines) were studied more intensively than other carboxylate derivatives. This is quite natural, since formate group is a C 1 ligand with composite structure and high reactivity.It is noteworthy that though separate IR and NMR parameters of Rh(I) carbonyl carboxylate complexes were reported in some of the above-mentioned papers, their comparison is difficult, since they were determined under different conditions. In this work, simple reaction is suggested that can be used to synthesize [ Rh ( µ -HCOO )( CO ) 2 ] 2 complex and its crystal structure is determined. The latter complex is shown to be suitable starting reagent in synthesis of Rh(I) carbonyl hydride HRh ( PPh 3 ) 3 ( CO ) . X-ray diffraction data available in the literature for bis(triphenylphosphine) complexes of the composition transRh ( RCOO )( PPh 3 ) 2 ( CO ) with R = H, CF 3 [13, 17] are supplemented with the data we obtained for analogous acetate complex. IR and NMR measurements of carbonyl formate complexes [ Rh ( µ -HCOO )( CO ) 2 ] 2 and of trans -Rh ( HCOO )( PPh 3 ) 2 ( CO ) together with their acetate and trifluoroacetate analogs made it possible to obtain for the first time a set of comparable spectral parameters that indicates a transfer of electronic effects of the ligands through a central atom. The results of this work were partially reported in the previous publications [20][21][22]. Abstract-Complexes[Rh(µ-RCOO)(CO) 2 ] 2 , where R = H, CH 3 , CF 3 (I, II, III, respectively) are synthesized by reacting anhyd...