Ligand and Metal Effects on the Formation of Main‐Group Polyhedral Clusters

Abstract

The reaction of AlMe3 or ZnMe2 with hppH (hppH=1,3,4,6,7,8‐hexahydro‐2H‐pyrimido[1,2‐a]pyrimidine) and then with tBuLi affords [Li8(H)m(hpp)6]n+[X]−n, X=[ZntBu3], m=n=1 (the cation core of which is shown); X=[Li(Me2AltBu2)2], m=0, n=2, as the major product in each case. These data reveal that non‐aromatic heterocycle hppH and ZnMe2 can be employed to generate novel hydride‐encapsulation main‐group‐metal clusters, and that related polylithium architectures can also incorporate a central void.

Metal‐Hydride Bonding in Higher Alkali Metal Boron Monohydrides

“…Hence, monomeric {4,6-tBu 2 C 6 H 4 -(CMe 2 CH 2 -2)BH(C 5 H 4 )}{CpMo(H) 2 }Li·TMEDA, [32] dimeric {(DMPE) 2 MoH(NO)·Et 3 BHLi} 2 (DMPE = bis(dimethylphosphanyl)ethane), [33] and polymeric {(DMPE) 2 -Mo(NO) 2 ·Et 3 BHLi} ϱ [34] all reveal B(µ-H)Li components, while (DMPE) 2 TaH 3 (µ-H) 2 ·Et 3 BHLi incorporates a core Ta(µ-H) 2 Li metallocycle linked to a B(µ-H)Li unit, [35] and {(DCHPB) 2 Ru(µ-H) 3 ·(s-Bu) 3 BHK} 2 {DCHPB = bis(dicyclohexylphosphanyl)butane} reveals both Ru(µ-H) 3 K and B(µ-H)K 2 motifs peripheral to a (KO) 2 core. [36] Core metallocycles of the type noted in (3) 2 and (4) 2 {that is K(µ-H) 2 K}, have been suggested previously only in the non-trivial 9-borafluorenyl "ate" dimer of 1-mesityl-5,7,9-trimethyl-9-hydro-9-borafluorenyl potassium that results from the reduction of 2,6-Mes 2 C 6 H 3 BBr 2 by KC 8 and also in the B-B-bonded diborate bis{1-(Trip-5,7-diisopropyl-9-hydro-9-borafluorenyl)}bis(potassium) that results from the comparable treatment of 2,6-Trip 2 C 6 H 3 BBr 2 . [21] In each of these two instances, the dimeric aggregates have been extensively supported by inter-monomer arene stabilization of the metal centers.…”

“…-[{PhN(2-C 5 H 4 N)} 6 -HLi 8 ] + , [5,6] X-ray analysis revealed encapsulation of the hydride center by a pseudocubic arrangement of alkali metal ions, each face of which was straddled by a bidentate amido ligand. The omission of lithium from the cluster has been noted, with the observation of neutral {PhN(2-C 5 H 4 N)} 6 HLi 7 and, of particular import in understanding the geometrical constraints of these systems, the use of hppH (= 1,3,4,6,7,8-hexahydro-2H-pyrimido[1,2-a]pyrimidine) [7] has recently allowed the comparison of [(hpp) 6 HLi 8 ] + with its hydride-free parent cluster [(hpp) 6 Li 8 ] 2+ .…”

“…The omission of lithium from the cluster has been noted, with the observation of neutral {PhN(2-C 5 H 4 N)} 6 HLi 7 and, of particular import in understanding the geometrical constraints of these systems, the use of hppH (= 1,3,4,6,7,8-hexahydro-2H-pyrimido[1,2-a]pyrimidine) [7] has recently allowed the comparison of [(hpp) 6 HLi 8 ] + with its hydride-free parent cluster [(hpp) 6 Li 8 ] 2+ . [8] Variation of hydride coordination in the field of Li 7/8 cubanes has been reported, with linear µ 2 -[Am = CyN(2-C 5 H 4 N), Cy = cyclohexyl], octahedral µ 6 -, capped-octahedral µ 7 -, and cubic µ 8 -bonding seen. [9] Attempts to vary the Lewis acid component in this chemistry led to the replication of hydride entrapment using boranes and shed light on the method of hydride production in Lewis acid-doped systems.…”

Structural Organozinc Chemistry

“…An X-ray crystal structure determination of the [t-Bu 3 Zn] − anion present in 21 62 has an almost perfect trigonal planar arrangement [Zn−C bond distances 2.080(7), 2.059(7) and 2.057(8)Å; C−Zn−C angles 118.1(2), 120.7(3) and 120.6 (3) • ]. Compound 21 was prepared by reacting 1,3,4,6,7,8-hexahydro-2H -pyrimido [1,2]pyrimidine, Me 2 Zn and tBuLi (equation 9).…”

Stabilisation of high oxidation-state niobium using ‘electron-rich’ bicyclic-guanidinates

“…doi:10.1016/j.jorganchem.2005.02.033 plane as the ÔCN 2 Õ amidine component in this molecule ensures a favourable alignment for overlap of the lone-pair with the empty p-orbital of the sp 2 -hybridised carbon. Previous work by ourselves and others have shown that the [hpp] À anion chelates to a range of different main group and transition metals [2], including lithium [3], aluminium [4], tin [5], zinc [6], yttrium [7] and titanium [8,9]. Crystallographic data for a series of mono-and bis-ligand compounds of titanium has indicated notably shorter Ti-N distances in [Ti(hpp)Cl 2 (l-Cl)] 2 and Ti(hpp) 2 Cl 2 when compared to the corresponding benzamidinate [10] and acyclic guanidinate [11] compounds.…”