Stepwise nucleophilic substitution of manganocene, syntheses and structures of the dimer [CpMn(hpp)]2and the unusual manganate cage [LiMn(hpp)3]2(hppH = 1,3,4,6,7,8-hexahydro-2H-pyrimido[1,2,a]pyrimidine)

Towards the Synthesis of Guanidinate- and Amidinate-Bridged Dimers of Mn and Ni

Reactions of Cp2M (Cp = cyclopentadienyl, M = Mn, Ni) with lithium amidinates and guanidinates are reported. The highly oxophilic nature of Mn leads to the isolation of the interstitial oxide Mn4O(MeN···CH···NMe)6 (4) in preference to the intended paddle-wheel homodimer Mn2(MeN···CH···NMe)4 when employing the sterically uncongested amidinate [MeN···CH···NMe]– ligand. In contrast, an analogous reaction using Cp2Ni yielded Ni2(MeN···CH···NMe)4 (5). The use of monoprotic guanidinate ligands also gave contrasting results for Mn and Ni. In the first case, the highly unusual spirocycle Mn{μ-NC(NMe2)2}4Li2·3THF (6) was produced in low yield. For M = Ni, use of the [hpp]– (1,3,4,6,7,8-hexahydro-2H-pyrimido[1,2-a]pyrimidinate) ligand gives results comparable with the synthesis of 5, with Ni2(hpp)4 (7) isolated. In contrast to recent data obtained using Cp2Cr, the guanidinate ligands do not sequester coformed CpLi. Density functional theory analysis corroborates the view that the intermetal distance in each of the reported dinickel paddle-wheel complexes (2.4846(8) and 2.3753(5) Å in 5 and 7 respectively) is defined by the geometric parameters of the bidentate ligands and that intermetal bonding is not present.

Reactions of Cp2M (M = Ni, V) with dilithium diamido-aryl reagents; retention and oxidation of the transition metal ions

The reactions of dilithium 1,2-diamidobenzene, [1,2-(HN)2C6H4]Li2 (L(1)H2)Li2, and dilithium 1,8-diamidonaphthalene, [1,8-(NH)2C10H6]Li2 (L(2)H2)Li2, with Cp2Ni and Cp2V have been used to obtain the new complexes (L(2)H2)2Ni{Li(THF)2}2 (3), (L(2)H2)3V{Li(THF)2}3 (4) and (L(1)H2)6Ni6·{[(L(1)H2)3(L(1)H)3Ni6Li(THF)](2-)·2[Li(THF)4](+)} (5), in which retention or oxidation of the initial metal(ii) centre is observed. Whereas 3 and 4 contain one transition metal ion within ion-paired structures, 5 has a complicated co-crystalline composition which contains octahedral Ni6-cages constructed from six square-planar (16e) Ni(II) centres.

The redox effect of the [1,2-(NH)2C6H4]2- ligand in the formation of transition metal compounds

Reactions of the [1,2-(NH)(2)C(6)H(4)](2-) dianion (LH(2)(2-)) with Cp(2)M(II) (M = V, Mn) lead to complete or partial oxidation of the metals (M), giving the V(III) compound [(η(5)-Cp)(LH(2))(2)VV(LH(2))](-)[Li(THF)(4)](+) (1) and Mn(II)(4)Mn(III)(2) oxo cage [Mn(6)(LH(2))(6)(μ(6)-O)(THF)(4)] (2).