Conformation-Associated C··· d z 2 -Pt II Tetrel Bonding: The Case of Cyclometallated Platinum(II) Complex with 4-Cyanopyridyl Urea Ligand.

The nucleophilic addition of 3-(4-cyanopyridin-2-yl)-1,1-dimethylurea ( 1 ) to cis -[Pt(CNXyl) 2 Cl 2 ] ( 2 ) gave a new cyclometallated compound 3 . It was characterized by NMR spectroscopy ( 1 H, 13 C, 195 Pt) and high-resolution mass spectrometry, as well as crystallized to obtain two crystalline forms ( 3 and 3 ·2MeCN), whose structures were determined by X-ray diffraction. In the crystalline structure of 3 , two conformers ( 3A and 3B ) were identified, while the structure 3 ·2MeCN had only one conformer 3A . The conformers differed by orientation of the N , N -dimethylcarbamoyl moiety relative to the metallacycle plane. In both crystals 3 and 3 ·2MeCN, the molecules of the Pt(II) complex are associated into supramolecular dimers, either { 3A } 2 or { 3B } 2 , via stacking interactions between the planes of two metal centers, which are additionally supported by hydrogen bonding. The theoretical consideration, utilizing a number of computational approaches, demonstrates that the C··· d z 2 (Pt) interaction makes a significant contribution in the total stacking forces in the geometrically optimized dimer [ 3A ] 2 and reveals the d z 2 (Pt)→π*(PyCN) charge transfer (CT). The presence of such CT process allowed for marking the C···Pt contact as a new example of a rare studied phenomenon, namely, tetrel bonding, in which the metal site acts as a Lewis base (an acceptor of noncovalent interaction).