A tungsten‐183 NMR study of cis and trans isomers of [W(CO) 4 (PPh 3 )(PR 3 )](PR 3 = 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 ν and θ (Tolman electronic factor and cone angle, respectively) for the cis isomers and to ν (but only poorly to θ) for the trans isomers. The 183 W 31 P spin coupling constant is also related, less clearly for PC than for PN and PO bonded ligands, to ν. Chemical shifts are referenced to an absolute frequency Ξ ( 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 © 2008 John Wiley & Sons, Ltd.