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 ButLi 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)NAlMe21 and this reacts with MeLi in thf to yield the simple ate complex Ph(2-C5H4N)NAlMe3Lthf 3, the employment of an organolithium substrate capable of -hydride elimination redirects the reaction significantly. Whereas the use of ButLi has previously yielded a main group interstitial hydride in which H¿ exhibits µ6-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/ButLi yields [{(c-C6H11)(2-C5H4N)N}6HLi8]+[(But2AlMe2)2Li]¿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/ButLi yields the µ8-hydride [(hpp)6HLi8]+[But3Zn]¿.5PhMe 7. Formation of the µ8-hydride [(hpp)6HLi8]+[ButBEt3]¿8 is revealed by employment of the system Et3B/ButLi. A new and potentially versatile route to interstitial hydrides of this class is revealed by synthesis of the mixed borohydride¿lithium hydride species [(hpp)6HLi8]+[Et3BH]¿10 and [(hpp)6HLi8]+[(Et3B)2H]¿12 through the direct combination of hppLi with Et3BHL