The perimidine skeleton provides a framework for the isolation of a novel, stable carbene possessing a unique molecular architecture and electronic structure. The remarkable steric environment and exceptional electron-donating ability for the carbene-carbon are revealed through structural and spectroscopic characterization of the parent carbene and two sterically encumbered rhodium-carbene complexes, L2RhCl{C[NCH(CH3)2]2(C10H6)} (5 L2 = COD; 6 L = CO).
A family of N,N‘-disubstituted perimidinium cation salts were employed as precursors to persistent
monomeric carbenes with novel molecular architectures and electronic structures. Depending on the
substituents, reaction of these 1,3-disubstituted perimidinium cations with LiN(SiMe3)2 led either to
deprotonation and generation of new carbenes or to enetetramines. In addition to spectroscopic
characterization, crystallographic analysis of C10H6(
i
PrN)2C (10), C10H6(
i
PrN)(Me3CCH2N)C (11), {C10H6[N(3,5-Me2C6H3)]2C}2 (13), and C10H6(
i
PrN)(3,5-Me2C6H3N)C (14) definitively confirmed the nature of
these species. The mixed benzyl/cycloheptyl-substituted carbene C10H6(cyclo-C7H13N)(p-MeC6H4CH2N)C
(17) was observed to undergo dimerization upon heating to yield both cis and trans isomers of the
enetetramine {C10H6(cyclo-C7H13N)(p-MeC6H4CH2N)C}2, (17)
2
. Rhodium complexes of these perimidine-based carbenes were accessed via reactions with either monomeric carbene or enetetramine. Spectroscopic
and crystallographic analysis of these rhodium−carbene complexes revealed the sterically demanding
nature of the carbene ligands, which is manifested in the observation of hindered Rh−Ccarbene bond rotation
and through %V
bur measurements, and their exceptional electron-donating ability.
The ambiphilic -phosphinoethylboranes Ph 2 PCH 2 CH 2 BR 2 (BR 2 ) BCy 2 (1a), BBN (1b)), which feature the ethano spacer CH 2 CH 2 between the Lewis acidic boryl and Lewis basic phosphino groups, were synthesized in nearly quantitative yields via the hydroboration of vinyldiphenylphosphine. Compounds 1a,b were fully characterized by elemental analysis and by NMR and IR spectroscopy. X-ray crystallographic studies of compound 1b revealed infinite helical chains of the molecules connected through P · · · B donor-acceptor interactions. The ability of these ambiphilic ligands to concurrently act as donors and acceptors was highlighted by their reactions with (dmpe)NiMe 2 . The zwitterionic complexes (dmpe)NiMe(Ph 2 PCH 2 CH 2 BCy 2 Me) (2a) and (dmpe)NiMe(Ph 2 PCH 2 CH 2 [BBN]Me) (2b) were generated via the abstraction of one of the methyl groups, forming a borate, and intramolecular coordination of the phosphine moiety to the resulting cationic metal center. Compound 2b was characterized by X-ray crystallography. Furthermore, B(C 6 F 5 ) 3 abstracts the methyl group of a coordinated borate ligand to generate a free, three-coordinate borane center in [(dmpe)NiMe(1a)] + [MeB(C 6 F 5 ) 3 ] -(3).
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