REACTIONS OF THE 12-ELECTRON ALKOXIDE-SUPPORTED TUNGSTEN CLUSTERS W4(OR)12 (R=CH2-I-PR, CH2-C-PEN) WITH ISOCYANIDES, NITRILES, NITRIC-OXIDE, AND ALKYNES - COMPARISON WITH THE REACTIVITY OF W2(OR)6 COMPOUNDS

The reactions between W4(OR)12 compounds, where R = CH2-i-Pr and CH2-C-Pen, and the isonitriles RNC, where R = t-Bu, PhCH2, and mesityl (2,4,6-C6H2Me3), in hydrocarbon solvents at 22-degrees-C yield the previously characterized mu4-carbido clusters W4(mu4-C)(OR)14 by cleavage of the C =N bond. Under similar conditions, the W4(OR)12 clusters are inert to the nitriles MeC=N and NC (CH2)5CN and to the internal alkynes MeC=CMe and EtC=CEt. The reaction between W4(OR)12 compounds and nitric oxide in hydrocarbon solutions at 22-degrees-C yields [W(OR)3-(NO)(py)]2 compounds in the presence of pyridine. The latter compound, where R = CH2-i-Pr, was characterized by an X-ray diffraction study. Crystal data for [W(OCH2-i-Pr)3(NO)(py)]2.2CH2Cl2 at -168-degrees-C: a = 9.559 (2) angstrom, b = 14.293 (4) angstrom, c = 17.435 (4) angstrom, beta = 93.75 (1)-degrees, Z = 8, d(calcd) = 1.669 g cm-3, space group = P2(1)/c. The molecule is centrosymmetric, and each tungsten atom is in an octahedral coordination environment. A pair of mu-OR bridges span a nonbonding W-to-W distance of 3.406 (1) angstrom. The W-N-O moiety is linear and the W-NO distance is short, 1.75 (1) A, which together with the low value of nu(NO), 1568 cm-1, are indicative of extensive W d(pi)-to-NO pi* back-bonding. These findings are compared with related reactions involving the dinuclear compounds W2(OR)6 (M=M) where R = i-Pr, t-Bu, and SiMe2(t-Bu).