Polyhedron Vol. 7, No. 18, pp. 178~1788,1988 Printed in Great Britain 0277-5387/88 163.00+.00 0 1988 Pergamon Press plc zyxwvutsr COMMUNICATION REACTION OF OXYGEN WITH A BINUCLEAR COBALT(I1) HEXAPHOSPHINE COMPLEX. SINGLE-CRYSTAL X-RAY STRUCTURE OF AN EXTENDED CHAIN COBALT(I1) HEXAPHOSPHINE OXIDE SYSTEM SUZANNE E. SAUM and FREDRIC R. ASKHAM Department of Chemistry, Washington University, St. Louis, MO 63130, U.S.A. and FRANK R. FRONCZEK and GEORGE G. STANLEY* Department of Chemistry, Louisiana State University, Baton Rouge, LA 70803-l 804, U.S.A. zyxwvutsrqponmlkjihgfedcbaZYXWVUTS (Received 22 February 1988 ; accepted 27 April 1988) Ahatract-Molecular oxygen reacts rapidly with Co2Cls_.(eHTP)Xf [x = 0 or 2 ; eHTP = (Et2PCH,CH&PCH2P(CH,CH,PEt,),] in dry acetonitrile to produce in approxi- mately 66% yield the fully-oxygenated phosphine oxide eHTP (eHTm) Co(I1) complex [Co(eHTP-_z’][CoC1:-]. The X-ray structure on this novel system shows an extended chain system in which the monomeric repeating unit has an octahedral Co(I1) centre. The eHTP=O ligand is adopting an unusual conformation with the phosphine oxide groups P(2)-P(l)--P(3) (P(1) is one of the internal phosphorus atoms) forming a P(l)-P(2) chelate to the metal atom while P(3) bridges to another Co(eHTP=O)*+ monomer unit making up the extended chain, instead of acting as an independent bis chelating group. The third unique coordination site on the cobalt centre is occupied by a phosphine oxide group from the other half of the eHTP=O ligand which bridges over to the cobalt centre forming a facial set of three p---O donor ligands. This mixed bridging/chelating conformation gives rise to fused seven- and nine-membered ring systems with a Co-Co separation of 7.613(O) A between symmetry related cobalt sites on the extended chain. This structure is the first reported for a Co(R,P=O)“,+ (R = alkyl, phenyl) system. Our investigations into the coordination chemistry of the hexaphosphine ligand, (Et,PCH2CHJ2 PCH,P(CH &H 2PEt &, eHTP, have demon- strated that it is a powerful binucleating agent for transition metal centres and we have characterized a number of dimer systems that exhibit a variety of coordination numbers, geometries and rotational conformations. ‘-’ These structural and con- formational studies have allowed us to gain a firmer *Author to whom correspondence should be addressed. understanding of the coordination properties and preferences of eHTP. The next stage in our inves- tigations is to study the reactivities of M,(eHTP) dimers to see if bimetallic cooperative effects can be observed and extended to catalytic cycles. The simple cobalt(I1) dimer, Co$l,_,(eHTP)“+ (x = 0 or 2), was the first eHTP complex characterized’ and now we would like to report on its clean reac- tion with molecular oxygen to produce the first crystallographically characterized cobalt per- alkylphosphine oxide complex. Two equivalents of CoCl, react quantitatively 1785