TRANSITION METAL COMPLEXES OF CONSTRAINED PHOSPHITE ESTERS .6. PHOSPHORUS-METAL STRETCHING FREQUENCIES IN METAL CARBONYL COMPLEXES OF POLYCYCLIC PHOSPHITES

The far-infrared spectra of complexes of the forms Ni(CO)4-xLx (x = 1, 2, 3, 4), Fe(CO)5-xLx (x = 1, 2), and cis- and trans-M(CO)6-xLx (x = 1, 2 and M = Cr, Mo, W) where L = P(OCH2)3CCH3, As(OCH2)3CCH3, orN(C2H4)3CH (quinuclidine) have been obtained and the absorption bands assigned to ligand vibrations, v(M-C), δ(M-C-0), and v(M-P), and bending modes of the general form δ(X-M-Y), where × and Y = C and C, C and P, C and N, or P and P. The preparations and characterization of the new complexes in this study are also given. Improved synthetic and purification techniques now allow an unambiguous assignment of the configurations from infrared data of the cis and trans group VI complexes of the type M(CO)4L2, where M = Cr, Mo, and W and L = P(OCH2)3CCH3 or P(OCH)3(CH2)3, The greater increase in r(M-P) from the mono- to the corresponding disubstituted trans-octahedral carbonyl complexes of P(OCH2)3CR (R = CH3 or (CH2)2-CH3) compared to the cis isomers is tentatively interpreted in terms of the number of π metal orbitals common to both phosphorus ligands and the probable relative π-bonding powers of the carbonyl and phosphorus ligands. The opposite trends in v(C-O) and v(M-P) in Ni(CO)4-xLx (L = PF8 or P(OCH2)3CCH3) upon stepwise substitution of the carbonyl groups are ascribed to the contrasting π-bonding abilities of these two ligands compared to those of a CO group. © 1968, American Chemical Society. All rights reserved.