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Homo‐ and Heterodimetallic Geminal Dianions Derived from the Bis(phosphinimine) {Ph 2 P(NSiMe 3 )} 2 CH 2 and the Alkali Metals Li, Na, and K
Author(s) -
Hull Katherine L.,
Carmichael Ian,
Noll Bruce C.,
Henderson Kenneth W.
Publication year - 2008
Publication title -
chemistry – a european journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.687
H-Index - 242
eISSN - 1521-3765
pISSN - 0947-6539
DOI - 10.1002/chem.200701976
Subject(s) - geminal , deprotonation , chemistry , crystallography , transmetalation , ligand (biochemistry) , octahedron , carbanion , alkali metal , stereochemistry , crystal structure , ion , catalysis , organic chemistry , biochemistry , receptor
The geminal organodimetallic complexes [({Ph 2 P(NSiMe 3 )} 2 C) 2 M 4 ], where M 4 =Na 4 , 3 ; Li 2 Na 2 , 4 ; LiNa 3 , 5 ; Li 2 K 2 , 6 ; Na 2 K 2 , 7 , and Na 3 K, 8 , have been prepared through a variety of methods including direct or sequential deprotonation of the neutral ligand with strong bases ( t BuLi, n BuNa, (Me 3 Si) 2 NNa, PhCH 2 K or (Me 3 Si) 2 NK), transmetalation of the homometallic derivatives (M 4 =Li 4 , 2 or Na 4 , 3 ) with t BuONa or t BuOK, and by cation exchange upon mixing the homometallic complexes in an arene solution. Complexes 3 – 8 have been characterized by single‐crystal X‐ray diffraction and are found to form a homologous series of dimeric structures in the solid‐state, in accord with the previously reported structure of 2 . Each complex is composed of a plane of four metals, M 4 , in which the ligands adopt capping positions to form distorted M 4 C 2 octahedral cores. The metals in homometallic complexes 2 and 3 define an approximate square, whereas the heterometallic derivatives 4 – 8 have distinctly rhombic arrangements. The lighter metals in 4 – 8 interact strongly with the carbanions and the heavier metals are pushed towards the periphery of the structures. 1 H, 13 C, 7 Li, 31 P, and 29 Si multinuclear NMR spectroscopic studies, cryoscopic measurements, and electrospray ionization‐mass spectroscopic studies are consistent with the dimers being retained in solution. Dynamic solution behavior was discovered for Li 2 Na 2 complex 4 , in which all five possible tetrametallic derivatives Li 4 , Li 3 Na, Li 2 Na 2 , LiNa 3 and Na 4 coexist. Density functional theory (DFT) and natural bond order (NBO) calculations in association with natural population analyses (NPA) reveal significant differences in the electronic structures of the variously metalated dianions. The smaller cations are more effective in localizing the double negative charge on the carbanion (in the form of two lone pairs), leading to differences in the distribution of the electron density within the ligand backbones. In turn, a complex interplay of hyperconjugation, electrostatics and metal‐ligand interactions is found to control the resulting electronic structures of the geminal organodimetallic complexes.