A tungsten-183 NMR study of cis and trans isomers of [W(CO)4(PPh3)(PR3)](PR3 = phosphine, phosphite)

Tungsten-183 NMR data are reported for the complexes cis- and trans-[W(CO)(4)(PPh(3))(PR(3))] (PR(3) = P(n)Bu(3), PMe(3), PMe(2)Ph, PMePh(2), PPh(3), P(4-C(6)H(4)OMe)(3), P(4-C(6)H(4)Me)(3), P(4-C(6)H(4)F)(3), P(OMe)(3), P(OEt)(3), P(OPh)(3) and for PCy(3), P(NMe(2))(3)(trans isomer only). The (183)W chemical shift (obtained by indirect detection using (31)P) is found to be related to the PR(3) ligand parameters nu and theta (Tolman electronic factor and cone angle, respectively) for the cis isomers and to nu (but only poorly to theta) for the trans isomers. The (183)W-(31)P spin coupling constant is also related, less clearly for P-C than for P-N and P-O bonded ligands, to nu. Chemical shifts are referenced to an absolute frequency Xi ((183)W) = 4.15 MHz, which is proposed as a calibration standard for (183)W NMR. The structures of cis-[W(CO)(4)(PPh(3))(PMe(3))] and cis-[W(CO)(4)(PPh(3)){P(4-C(6)H(4)F)(3)}] are reported. Copyright (C) 2008 John Wiley & Sons, Ltd.