Polyhedr on Vol. 5, No. 12, pp. 2081-2091,1986 Printed in Great Britain 0277-5387/86 S3.00+ .OO 0 1986 Pergamon Journals Ltd STUDIES OF x-BONDING PERTURBATION IN THE TUNGSTEN-NITROGEN MULTIPLE BOND OF ISOPROPYLIMIDO TUNGSTEN(W) COMPLEXES : THE CRYSTAL AND MOLECULAR STRUCTURES OF Iw(NCI-IMeW~12 l Cd& AND WoVC~ GUINEt 4 1 BARRY R. ASHCROFT, GEORGE R. CLARK, ALASTAIR J. NIELSON* and CLIFTON E. F. RICKARD Department of Chemistry, Auckland University, Private Bag, Auckland, New Zealand (Received 11 M arch 1986 ; accepted 19 May 1986) Abstract-‘3C NMR chemical shift data for the a-carbon (6,) of a variety of tungsten isopropylimido complexes indicate that the extent to which the nitrogen lone pair par- ticipates in multiple bonding to tungsten depends on the form of the complex and the ligands involved. The structures of [W(NCHMe2)C1&* C6H6 (la) and [W(NCHMez)Cl,]wEt43] (7) which show widely different 6, values, have been determined by single-crystal X-ray diffraction methods. Crystals of la are triclinic space group PI, with a = 6.394(2), b = 8.890(3), c = 11.205(2) 8, and a = 109.95(2)“, fi = 98.91(2)“, y = 93.96(2)” ; crystals of 7 are orthorhombic, space group Prima, with a = 13.667(5), b = 15.152(2), c = 9.432(2) A. Both structures were solved by Patterson and Fourier methods and refined to an R value . of 0.050 for 1325 observed data of la and to an R value of 0.050 for the 1157 observed data of 7. Complex la is dimeric with a W-N bond length of 1.697(12) 8, and complex 7 is monomeric with a longer W-N bond length of 1.763(16) A. Comparison of the W-Cl bond lengths and correlations with n-bonding to make an 18-electron count, indicates that the W-N bond lengths differ in the two complexes as a result of overall x-bonding requirements. The multiple bond of organoimido complexes (M=NR)’ has not shown the diversity of reactions exhibited by the related alkylidene and alkylidyne complexes (M=CHR and M&R)’ and in general is comparatively unreactive. Electrophilic activity has been observed to occur for osmium organo- imido complexes where the amination of olefins is now well known3 and also in the reactions of Cr(N- t-Bu)2(OSi&4e3)2with Ph2Zn.4 Nucleophilic activity has been identified in the reaction of M=NR com- plexes with PhCHO to give Ma complexes and PhCH=NR5 while Mo(NPh)2(S2CNEt2)2 reacts with MeBr to give Mo(NPh)Br2(S2CNEt2)2.6 These reactions have mainly been identified by analysis of the organic products produced but some examples of the intermediate complexes are now emerg- ing. The alkanolaminato osmiurn(V1) complex 0s204(0CMe2CH2NBu’)z has recently been charac- *Author to whom correspondence should be addnwed. terised by X-ray crystallography7 as have the amido complexes [W2(NHPh)2@-pinacol)(pinacol)4]8 and [W(NCMe3)(NHCMe3)2(benzopinacol)]T which result from protonation of an imido function. One approach taken to increase the nucleo- philicity of the imido nitrogen has been the prep- aration of complexes in which the maximum electron count can exceed 18 electrons, either by placing a strongly competitive z-donating ligand tram to the imido function as in the case of [Re(NPhCH3)(OEt)(S2CNMe2)~10 or by intro- ducing a second imido function which is forced to act essentially as a two-electron donor (i.e. M=NR) as in the case of [Mo(NPh)2(S2CNEt2)&1’ Alternatively, 13C NMR investigations of a series of 8 t-butylimido complexes have shown that on changing the metal, the charge on the imido nitrogen atom decreases on proceeding upwards and to the right of the transition metal series.12 In view of these studies we were interested in 2081