Synthesis and study of Pt(II)–nitrile complexes. Multinuclear NMR spectra and crystal structures of compounds of the types [Pt(R-CN)Cl₃]⁻ and cis and trans-Pt(R-CN)₂Cl₂

Abstract

Abstract:Complexes of the type [Pt(R-CN)Cl,]-were synthesized and studied by 'H, ' ", and Ig5pt NMR spectroscopies. The " J ( '~~P~- '~C ) coupling constants are about 240 Hz. The signals due to the cyano carbon atoms of the coordinated ligands were observed at higher fields than those of the free ligands. The shielding on the cyano carbon increases as the alkyl chain lengthens and also when the branching increases. The lg5pt signals of all the complexes were observed around -2000 ppm. The crystal structures of (NMe,)[Pt(C,H,-CN)Cl,] (1) and (NMe4)[Pt(p-HO-C6H,-CN)C13] (2) were determined. Con~pound 1 is monoclinic, P2,/c, a = 8.384(5), b = 15.336(19), c = 11.759(9) 8,, P = 99.52(6)", Z = 4, R = 0.054, and IVR = 0.051. Crystal 2 is tetragonal with a = 16.222(6), c = 12.052(5) 8,, Z = 8, R = 0.059, and wR = 0.044. The Pt-CI bond trans to the nitrile ligand is shorter than normal (2.276(3) 8, for 1 and 2.264(7) A for 2) while the two other bonds are normal (2.293(4), 2.287(3) 8, for 1 and 2.320(7), 2.275(8) 8, for 2). The Pt-N bonds are 1.97(1) 8, (1) and 1.92(2) 8, (2) and the segments Pt-N=C-C are linear.Disubstituted compounds were also synthesized and studied by multinuclear NMR. The ' "~t signals of the cis isomers were observed at lower fields than those of the trans isomers (A = 65 ppm), while the 13c signals of the cyano carbons of the trarzs isomers were observed at lower fields than those of the cis compounds (A = 0.6 pprn). The cis complexes isomerize to the trans compounds upon heating. The crystal structures of cis-(3) and trans-Pt(C2H5-CN),C12 (4) and also of cis-Pt@-HO-C,H,-CN),Cl, (5) Author to whom correspondence may be addressed. Telephone: (514)

Synthesis and characterisation of mixed ligand Pt(ii) and Pt(iv) oxadiazoline complexes

“…22 This method was chosen to favour formation of the trans-configured compound due to thermal conversion of the kinetic cis-into the thermodynamically more stable transform (or an equilibrium mixture of them). [22][23][24] The cis-and transforms of PtBr 2 (PhCN) 2 25,26 and PtI 2 (PhCN) 2 27 have been prepared previously, but their characterisation involved IR and Raman spectroscopy only. Using our protocol, uniform samples of trans-2b and trans-2c are obtained, which resemble the corresponding trans-isomer of PtCl 2 (PhCN) 2 very closely with respect to their spectroscopic data and also in their chromatographic behaviour.…”

Cycloaddition of nitrones to free and coordinated (E)-cinnamonitrile: effect of metal coordination and microwave irradiation on the selectivity of the reaction

“…The 195 Pt resonance at Ϫ2268 ppm is in between the values found for the bis-cycloaddition product 4a and the expected position of [PtCl 2 (nitrile) 2 ] complexes. 22 The fact that the mono-cycloaddition product is formed selectively is attributed to the different extent of Lewis acid activation the platinum centre exhibits. In the starting complex [PtCl 2 (cinnamonitrile) 2 ], the Pt centre is a stronger Lewis acid, because all coordinated ligands, Cl as well as the nitriles, are electron withdrawing, and this is expected to result in a high activation of the C᎐ ᎐ ᎐ N bond.…”

Platinum(iv)-mediated hydrolysis of nitriles giving metal-bound iminols

“…In the chemistry of platinum, to date only the hydroxide-promoted hydrolysis of organonitriles has been described. [22][23][24][25][26][27] Hence, a separate study on the addition of water to organonitriles mediated by a platinum() centre was thought to be timely.…”