Synthesis and Molecular Structure of [Fe-4(CO)(10)(mu(4)-O)(kappa(K)2-dppn)] (dppn=1,8-bis(diphenylphosphino)naphthalene): A Missing Piece in the [M-4(CO)(12)(mu(4)-E)](n-) (M = Fe, Ru:E = C, N, O; n=2, 1, 0) Puzzle

Reaction of Fe-3(CO)(12) with 1,8-bis(diphenylphosphino)naphthalene (dppn) yields the tetranuclear oxide cluster [Fe-4(CO)(10)(mu(4)-O)(kappa(2)-dppn)] (1), which has been crystallographically characterized. It is a member Of the [M-4(CO)(12)(mu(4)-E)](n-) series of butterfly clusters, being a close relative of the unknown "missing link" [Fe-4(CO)(12)(mu(4)-O)] (2). In Order to Understand the stability of' I relative to 2, we have carried out DFT calculations oil [Fe-4(CO)(10)L-2(mu(4)-O)] (L = CO, PMe3, PPh3; L-2 = dppn), which suggest that I is best considered its a combination of [Fe-3(CO)(9)O](2-) and [Fc(CO)(dppn)](2+) fragments.