[(ETA(5)-C(5)R(5))CRR](N) - A NEW CLASS OF PARAMAGNETIC ALKYLS AND HYDRIDES OF DIVALENT CHROMIUM

[CpCr-II(mu-Cl)](2) (1), prepared by reduction of [Cp*Cr-III(mu-Cl)Cl ](2) with Li[HBEt(3)] or by reaction of Cr-II-Cl-2 with CpLi, served as the precursor for the synthesis of a series of dinuclear chromium(I I) alkyls of the type [CpCrII(mu-R)](2)(R = Me (2), Et (3), (n)Bu (4) , Ph (5), CH(2)SiMe(3) (6)). They feature short Cr-Cr distances, low m agnetic moments, and attenuated reactivity, consistent with strong met al-metal banding. 3 decomposed in benzene to yield [(CpCr-II)(2)(mu-E t)(mu-Ph)] (7), and 2 reacted with O-2 to give both CpCr-VI(O)(2)Me a nd [(CpCr-V(O)Me)(2)(mu-O)] (8). Hydrogenolysis of [Cp''Cr-II(mu-Me]( 2) (2a, Cp'' = eta(5)-C(5)Me(4)Et) first yielded paramagnetic [Cp''Cr- II(mu(3)-H)](4) (9); however, pure 9 must be prepared by reaction of [ Cp''Cr-II(mu-Cl)](2) (1a) with Li[HBEt(3)]. The structure of 9 has bee n redetermined due to a compositional disorder problem of the original determination. The identification of 9 as a tetrahydride rests on pro tonation experiments and the C-13 NMR observation of five isotopomers [(Cp''Cr-II)(4)(H-4-x)(D)(x)], resulting from WD exchange. The molecul ar structures of 1, 2, 7, 8, and 9 have been determined by X-ray diffr action.