A variety of donor adducts of tris(pentafluorophenyl)borane were experimentally generated by reaction of a Lewis base with an excess of B(C6F5)3 in pentane. In this way, nitrile complexes (C6F5)3B·NCR (R = CH3 1a, p-CH3−C6H4 1b, p-NO2−C6H4 1c), isonitrile complexes (C6F5)3B·CNR (R = C(CH3)3 3a, C(CH3)2CH2C(CH3)3 3b, 2,6-(CH3)2−C6H3 3c), and the phosphine adduct (C6F5)3B·P(C6H5)3 (6) could be prepared. The compounds were characterized by IR and NMR spectroscopy and by X-ray structure analyses (1a, 1c, 3a, 3b, and 6). Coordination of the nitriles as well as the isonitriles to the neutral Lewis acid leads to a substantial increase in the C⋮N bond strength. This is evident from a marked shift of the ν̃C ⋮ N IR band to higher wavenumbers, and this interpretation is supported by the small but experimentally significant decrease of the C⋮N bond length observed by X-ray diffraction. The experimental work is complemented by a density functional study on the model complexes (C6F5)3B·L, L = CNCH3, NCCH3, PH3, CO. A detailed analysis revealed that the bonding in (C6F5)3B·L complexes is mainly dominated by electrostatic interaction, which in turn is responsible for the observed structural and spectroscopic changes. In the context of this work, the bonding of the neutral B(C6F5)3 Lewis acid is compared to the positively charged organometallic d0-Cp3M+ system (M = Zr, Hf). It was found that electrostatic effects are more pronounced for B(C6F5)3 than for the transition metal fragments. The question as to the existence of a nonclassical main group carbonyl complex, (C6F5)3B·CO, is addressed.

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N-Heterocyclic carbene complexes of platinum (II) have been synthesized, notably monocarbene complexes cis-[(IPr)Pt(dmso)(Cl) 2 ], 6, cis-[(IMes)Pt(dmso)(Cl) 2 ], 7, cis-[(SIPr)Pt(dmso)(Cl) 2 ], 8, cis-[(SIMes)Pt(dmso)(Cl) 2 ], 9, and cis-[(TTP)Pt(dmso)(Cl) 2 ], 10. All complexes have been fully characterized by multinuclear NMR spectroscopy. Complex 7, 9, and 10 have been characterized by X-ray crystallography. The data obtained have allowed for the differentiation between electronic contributions (σ and π) present in the Pt-NHC bond. Supported by computational analyses, the percentage of π backdonation from the metal to the NHC is found to be on the order of 10%. More interestingly, we find that saturated NHC (SIPr and SIMes) are more efficient π back-acceptors than their unsaturated NHC congeners (IPr and IMes). The synergistic effect between π back-donation and σ donation present in the saturated NHC systems results in increased electron density at the platinum center compared to the bonding situation in the unsaturated NHC examples.