Interconverting WW Triple Bonds and W4 Clusters: Structures of W4(OPr n )16 and [Li2W2(OPr n )8(DME)]2*

摘要

Alcoholysis of W2(NMe2)6 with excess n-propanol in hexane yields the tetranuclear cluster, W4(OPrn, I. Reduction of I with two equivalents of Li2COT in THF gives a small yield of Li2W2(OPrn)8. Single crystals were isolated by cooling the product mixture in DME and were shown to be [Li2W2(OPrn)8(DME)]2, II, which consists of a unique “dimer of dimers” structure. In this reaction sequence, W 4 16+ cluster formation is followed by four electron reduction to reform the (W≡W)6+ unit. Better yields of the lithium salt can be obtained by the addition of LiOPrn/HOPrn solutions to W2(OBut)6 in which case Li2W2(OPrn)8 has been obtained as a 1:1 adduct with LiOPr. This identity of this salt was confirmed by solution NMR spectroscopy. In the alternative reaction, the (W≡W)6+ center remains intact from reactant to product. No attempt has been made to separate the product from excess LiOPr. DFT (ADF 2004.01) molecular orbital calculations on the model cluster W4(OH)16 are used to help elucidate the disruption of the W4 cluster upon four electron reduction. The molecular structures of compounds I and II are reported.