Polyhedron Vol. 12, No. 22, pp. 2741-2743. 1993 Printed in Great Britain 0277-5387/93 $6.00+.00 C? 1993 Pergamon Press Ltd zyxwvutsr COMMUNICATION zyxwvutsrqponmlkjihgfedcbaZYXWVUT A STERIC PREFERENCE FOR LINEAR VERSUS BENT IMIDO LIGATION? SYNTHESIS AND X-RAY CRYSTAL STRUCTURE OF [Mo(NAr),(edtc),J(Ar = 2$iiPr,C6H, ; edtc = S2CNEt2) CONTAINING TWO LINEAR IMIDO MOIETIES THfiR@SE A. COFFEY, GLYN D. FORSTER, GRAEME HOGARTH* and ANDREA SELLA Chemistry Department, University College London, 20 Gordon Street, London WClH OAJ, U.K. (Received 26 July 1993; accepted 31 August 1993) Abstract-Reaction of two equivalents of ArNCO (Ar = 2,6-‘Pr,C,H,) with [Mo0,(edtc)2] affords the bisimido complex [Mo(NAr),(edtc),] shown by crystallography to contain two linear imido ligands ; this is in contrast to the parent complex [Mo(NPh),(edtc),] previously shown to contain both linear and bent imido groups. Complexes containing the imido ligand continue to attract considerable attention, primarily since they are envisaged as potential amination and azi- ridination reagents for organic synthesis. It is well documented that, depending upon the metal-nitro- gen-carbon angle, the ligand may act as either a 2- or 4-electron donor to a metal centre, and this is easily understood in terms of the simple valence bond models.’ More recently, a number of studies have considered the bonding in such complexes in more detail and concluded that when more than one imido ligand is present, the donor ability may *Author to whom correspondence should be addressed. iComplex zyxwvutsrqponmlkjihgfedcbaZYXWVUTSRQPONMLKJIHGFEDCBA 1 was characterized by elemental analyses and IR and NMR (‘H and 13C)spectra. Selected data : ‘H NMR. (C7D8, 373 K) 6 6.95 (d, 4H, J 7.6, m-C,H3), 6.80 (t, 2H, J 7.6, p-&H,), 4.08 (septet, 4H, J6.8, Chime,), 3.46 (q, 8H, J7.0, CH,Me), 1.19 (d, 24H, J6.8, CHMe& 0.96 (t, 12H, J7.0, CH,Me); (C7D8, 253 K) 6 6.96 (d, 4H, J 7.6, m-C,H3), 6.84 (t, 2H, J 7.6, p-C6H3), 4.17 (septet, 4H, J 6.8, Chime,), 3.47 (sextet, 2H, J 6.8, CH,Me), 3.14 (m, 4H, &?&Me), 2.93 (sextet, 2H, C&Me), 1.28 (d, 12H, J6.8, CHMe,), 1.16 (d, 12H, J 6.8, CHMe2), 0.81 (t, 6H, J 6.8, CH,Me), 0.74 (t, 6H, J 7.0, CH,Me); IR (KBr) 1267s, 1210m, 1149m, 1095w, 1075m, 962m, 847w, 755s cm-‘. Satisfactory elemental analyses were obtained. be intermediate between these two valence bond extremes.2*3 An interesting dilemma arises for a mol- ecule that contains two imido ligands, from which the metal requires only six electrons. This is the case for complexes of the stoicheiometry [Mo(NR),L,] (where L is a three electron donor ligand), since the MoL2 moiety is a 12 electron fragment. To date only one complex of this type has been structurally characterized, namely [Mo(NPh),(edtc),], shown to contain one bent and one linear imido ligand.4 We now report the synthesis and structure of another compound of this stoicheiometry which differs only in the steric bulk associated with the aryl group, but adopts a structure in which both imido ligands are linear. Addition of two equivalents of 2,6-diiso- propylphenylisocyanate to a toluene solution of [MoO,(edtc),] affords after chromatography the bisimido complex [Mo(NAr),(edtc),] 1 in 50% yield.? Addition of only one equivalent of aryl- isocyanate also yielded 1 as the major product and the mixed oxo-imido complex was not isolated, indicating that the second substitution process occurs considerably faster than the first. MoO,(edtc), + 2 ArNC0-r Mo(NAr),(edtc)z+ 2C02 2741