Nucleophilic Attack of Amides onto Coordinated Ethylene in Platinum Complexes Supported by a Chelating Pyridyl−Pyrrolide Ligand: Azaplatinacyclobutane and Vinylamine Complexes

The platinum ethylene complexes (PyPyr)Pt(C2H4)Cl (1) and (PyPyr)Pt(C2H4)OTf (4) (PyPyr = 3,5-diphenyl-2-(2-pyridyl)pyrrolide) were treated with 1 equiv of LiN(SiMe3)2, LiNiPr2, and LiNH(o-xylyl) to produce the platinum complexes (PyPyr)PtH[η2-CH2═CHN(SiMe3)2] (5), (PyPyr)Pt[κ2C,N-(CH2CH2NiPr2)] (6), and (PyPyr)Pt{κ2C,N-[CH2CH2NH(o-xylyl)]} (7), respectively. X-ray crystallography reveals that 7 adopts a square-planar geometry at the platinum center and the azaplatinacyclobutane ring displays a puckering of the β-carbon out of planarity by 0.270 Å. Thermolysis of 5 and 7 at 60 °C for 16 h releases the vinylamines (CH2═CH)N(SiMe3)2 and (CH2═CH)NH(o-xylyl), respectively. Heating 5 and 7 under 1 atm of H2 at 60 °C releases the ethylamines EtN(SiMe3)2 and EtNH(o-xylyl), respectively. Addition of PiPr3 to 7 produces (PyPyr)Pt(PiPr3)[CH2CH2NH(o-xylyl)] (8) in 95% yield, while additions of 1 equiv of a Lewis base (L) to 1 result in displacement of ethylene to give (PyPyr)Pt(L)Cl (L = NEt3 (9), NH2Ph (10), PiPr3 (11)). The amido complex (PyPyr)Pt(PiPr3)[NH(o-xylyl)] (12) results from treament of 11 with LiNH(o-xylyl), and 12 does not undergo ethylene insertion into the Pt−N bond under 1 atm of C2H4 at 120 °C over 3 days. Addition of 1 equiv of LiNH(o-xylyl) to (PyPyr)Pt(SMe2)Cl (2) produces the μ-amido-bridged dimer [(PyPyr)Pt(μ-NH(o-xylyl))]2 (13), and treatment of 13 with 2 equiv of iPr3P produces 12. These reactivity studies are consistent with a mechanism for the formation of 5−7 involving nucleophilic attack of an amide onto coordinated olefin.