EVALUATION OF THE 2,6-DIISOPROPYLPHEYLIMIDO LIGAND AS A STERIC FORCE IN D(1) AND D(2) MONOMERIC OCTAHEDRAL COMPLEXES OF TUNGSTEN

Reduction of [{WCl4(NC6H3Pr2i-2,6)}(2)] with 2 equivalents of Na-Hg am algam in the presence of phosphines gave the d(1) complexes [WCl3(NC6H 3Pr2i-2,6)L(2)] (L = PMe(3), PMe(2)Ph or PMePh(2)). The crystal struct ure of [WCl3(NC6H3Pr2i-2,6)(PMe(3))(2)] 1 shows the 2,6-diisopropylphe nylimido ligand exerts a greater trans influence than a phenylimido li gand but only slightly more steric pressure. Solutions of complex 1 re act with air to give [WCl3(NC(6)H(3)Pr(2)(-)2,6)(PMe(3))(OPMe(3))] 2 f or which the crystal structure shows the OPMe(3) ligand lying trans to the imido ligand. Reduction of [{WCl4(NC6H3Pr2i-2,6)}(2)] with 4 equi valents of Na-Hg amalgam in the presence of phosphines gave the d(2) c omplexes [WCl2(NC(6)H(3)Pr(2)(-)2,6)L(3)] (L = PMe(3) or PMe(2)Ph). Co mplex [WCl2(NC6H3Pr2i-2,6)(PMe(3))(3)] 3 reacts with alkynes L' to giv e the complexes [WCl2(NC6H3Pr2i-2,6)L'(PMe(3))(2)] (L' = PhC(2)Ph, MeC (2)Me or PhC(2)H) for which H-1 and C-13-{H-1} NMR spectral data were obtained. The crystal structure of [WCl2(NC6H3Pr2i-2.6)(PhC(2)H)(PMe(3 ))(2)] 6 shows cis-chloro ligands, trans-phosphines and mutually cis-i mido and alkyne ligands. The C(6) isopropyl group rotates to minimise the isopropyl group and PhC(2)H interaction. The complex [WCl2(NC6H3Pr 2i-2.6)(PhC(2)Ph)(PMe(2)Ph)(2)] can be prepared but not [WCl2(NC6H3Pr2 i-2,6)(PhC(2)Ph)(PMePh(2))(2)]. Reduction of [WCl3(NC6H3Pr2i-2.6)(PMe( 3))(2)] by Na-Hg amalgam in the presence of olefins gave the complexes [WCl2(NC6H3Pr2i-2,6)L'(PMe(3))(2)] (L' = CH2CH2 or CH(2)CHMe). A more bulky organoimido ligand or a large phosphine is needed to exert ster ic pressure in all the complexes prepared.