Diversity of Isomerization Patterns and Protolytic Forms in Aminocarbene Complexes


Diversity of Isomerization Patterns and Protolytic Forms in Aminocarbene PdII and PtII Complexes Formed upon Addition of N,N’-Diphenylguanidine to Metal-activated Isocyanides




Full text: Organometallics, 2017, 36 (21), pp 4145–4159



In this work we found that reaction of the palladium(II) and platinum(II) isocyanide complexes cis-[MCl2(CNR)2] [M = Pd, R = C6H3(2,6-Me2) (Xyl), 2-Cl-6-MeC6H3, cyclohexyl (Cy), t-Bu, C(Me)2CH2(Me)3 (1,1,3,3-tetramethylbuth-1-yl abbreviated as tmbu); M = Pt, R = Xyl, 2-Cl-6-MeC6H3, Cy, t-Bu, tmbu] with N,N’-diphenylguanidine (DPG) leads to DPG-derived metal-bound acyclic diaminocarbene (ADC) species. 


This reaction occurs via the two-step process, involving the initial coupling of the guanidine with one of the isocyanides and leading to monocarbene monochelated species, while the next addition grants the bis-carbene bis-chelated metal compounds; DPG behaves as nucleophile, deprotonating base, and chelator. The addition of DPG proceeded with different regioselectivity depending on the metal center and, in a larger extent, on the substituent R in RNCs. The X-ray diffraction studies for the mono- and bis-carbene complexes confirmed the regioisomerism of these species and allowed the identification of ADC protolytic forms stabilized in the solid-state. 1D (1H and 13C{1H}) and 2D (1H,1H-NOESY; 1H,15N-HSQC; 1H,15N-HMBC) solution NMR of the obtained systems demonstrated their configuration isomerism accompanied with prototropic tautomerism. Together, the solid state and solution data provide an insight into the flexible character of ADC species.







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