Chemistry of cis-bis(2,2′-bipyridine)dicarbonyl-molybdenum(0) and -tungsten(0). Substitution reactions with phosphorus donor ligands and with lsocyanides

Abstract

Nucleophilic substitution reactions of cis-[M(CO)₂(bipy)₂](M = Mo or W; bipy = 2,2′-bipyridine) by various unidentate (PR₃; R = Ph, Buⁿ, or OMe) and bidentate (Ph₂PCH₂CH₂PPh₂= dppe) phosphorus and carbon (CNR; R = Et or p-tolyl) donor ligands, L, result in displacement of bipy to produce cis,trans-[Mo(CO)₂L₂(bipy)](L = PR₃), cis,cis-[M(CO)₂L₂(bipy)][M = Mo, L₂=(CNEt)₂ or dppe; M = W, L = CNEt], cis-[M(CO)₂L₄](M = Mo or W; L = CNC₆H₄Me-p), and fac-[Mo(CO)₃L(bipy)](L = PPh₃) depending on the ligand L, temperature, and solvent. Trifluorophosphine reacts with cis-[Mo(CO)₂(bipy)₂] to displace CO and form cis-[Mo(PF₃)₂(bipy)₂]. Substitution in [M(CO)₄(bipy)] by isocyanides gives fac-[M(CO)₃(CNR)(bipy)](M = Cr; R = Et or p-tolyl; M = Mo, R = Et) or cis-[Mo(CO)₄(CNR)₂](R =p-tolyl). The products are characterised by microanalysis and by i.r., ¹H and ³¹P n.m.r. electronic, and mass spectroscopy. It is suggested that the formation of cis,trans-[Mo(CO)₂L₂(bipy)] may involve a trigonal biprismatic intermediate structure which allows reorganisation to occur simply. The acceptor strength of L in [Mo(CO)₂L₂(bipy)] indicated by i.r. [ν(CO)], ¹H n.m.r. (bipy ring chemical shifts), and visible (Mo → bipy dπ*) spectra, decreases in the order CO > P(OMe)₃ > CNEt > PBu₃ > bipy, which does not reflect geometrical differences in the disposition of these ligands.