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

Reaction of the palladium(II) and platinum(II) isocyanide complexes cis -[MCl 2 (CNR) 2 ] [M = Pd, R = C 6 H 3 (2,6-Me 2 ) (Xyl), 2-Cl-6-MeC 6 H 3, cyclohexyl (Cy), t -Bu, C(Me) 2 CH 2 (Me) 3 (1,1,3,3-tetramethylbuth-1-yl abbreviated as tmbu); M = Pt, R = Xyl, 2-Cl-6-MeC 6 H 3, Cy, t -Bu, and tmbu] with N, N ′-diphenylguanidine (DPG) leads to DPG-derived metal-bound deprotonated acyclic diaminocarbene (ADC) species. This reaction occurs via a two-step process, involving the initial coupling of the guanidine with one of the isocyanides and leading to deprotonated monocarbene monochelated species, while the next addition grants the deprotonated 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 deprotonated 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 ( 1 H and 13 C{ 1 H}) and 2D ( 1 H, 1 H-NOESY; 1 H, 15 N-HSQC; 1 H, 15 N-HMBC) solution NMR of the obtained systems demonstrated their configuration isomerism accompanied by prototropic tautomerism. Together, the solid-state and solution data provide an insight into the flexible character of ADC species.