Reactions of tungsten(VI) dialkyl complexes with Bu-t NC: Synthesis and characterization of new square pyramidal and trigonal bipyramidal tungsten(VI) complexes

The complexes [(TMS)(2)pda](NPh)WR2((TMS)(2)pda = o-(Me3SiN)(2)C6H4}(2-); R = CH3 (1), CH2-CMe3 (4)) react with (BuNC)-Bu-t to form the octahedral mono adducts [(TMS)(2)pda](NPh)WR2(CNt-Bu) (1a and 4a). la is observed only at low temperature, while 4a can be isolated. Both la and 4a react with (BuNC)-Bu-t to form the corresponding trigonal bipyramidal bis(eta(2)-imino-acyl) species [(TMS)(2)pda] (NPh)W[eta(2)-(Bu-t)NCR](2) (R = CH3 (2), CH2CMe3 (5)), which have been isolated and characterized. Compound 2 isomerizes upon heating to the square pyramidal metallacycle [(TMS)(2)pda](NPh)W[(Bu-t)NC(CH3)=C(CH3)N(Bu-t)] (3), which has been isolated as a red solid. X-ray crystal structures have been obtained for compounds 2 and 3. Crystals of 2 are orthorhombic, space group P2(1)2(1)2(1), with a = 9.1175(3) Angstrom, b = 17.9587(5) Angstrom, c = 20.9435(6) Angstrom, and Z = 4. Compound 2 has trigonal bipyramidal geometry with the imido N and one amido N in axial positions. Crystals of 3 are monoclinic, space group C2/c, with a = 35.1302(9) Angstrom, b = 12.6459(2) Angstrom, c = 16.2386(6) Angstrom, beta = 112.021(3)degrees, and Z = 8. 3 has distorted square pyramidal geometry with the imido moiety in the apical position.