Encapsulation of hydride by molecular main group metal clusters: manipulating the source and coordination sphere of the interstitial ion

The sequential treatment of Lewis acids with N,N'-bidentate ligands and thereafter with (BuLi)-Li-t has afforded a series of hydride-encapsulating alkali metal polyhedra. While the use of Me3Al in conjunction with Ph(2-C5H4N)NH gives Ph(2-C5H4N)NAlMe2 1 and this reacts with MeLi in thf to yield the simple'ate complex Ph(2-C5H4N)NAlMe3Li.thf 3, the employment of an organolithium substrate capable of P-hydride elimination redirects the reaction significantly. Whereas the use of ButLi has previously yielded a main group interstitial hydride in which H- exhibits mu(6)-coordination, it is shown here that variability in the coordination sphere of the encapsulated hydride may be induced by manipulation of the organic ligand. Reaction of (c-C6H11)(2-C5H4N)NH with Me3Al/(BuLi)-Li-t yields [{(c-C6H11)(2-C5H4N)N}(6)HLi8](+)[((Bu2AlMe2)-Al-t)(2)Li](-) 6, which is best viewed as incorporating only linear di-coordination of the hydride ion. The guanidine 1,3,4,6,7,8-hexahydro-2H-pyrimido[1,2-a]pyrimidine (hppH) in conjunction with Me2Zn/(BuLi)-Li-t yields the mu(8) hydride [(hpp)(6)HLi8](+)[(Bu3Zn)-Zn-t](-).PhMe 7, Formation of the mu(8)-hydride [hpp(6)HLi(8)](+)[(BuBEt3)-B-t](-) 8 is revealed by employment of the system Et3B/(BuLi)-Li-t. A new and potentially versatile route to interstitial hydrides of this class is revealed by synthesis of the mixed borohydride-lithium hydride species [hpp(6)HLi(8)](+)[Et3BH](-) 10 and [hpp(6)HLi(8)](+)[(Et3B)(2)H](-) 12 through the direct combination of hppLi with Et3BHLi.