Oxidative-addition reactions of cyclometallated platinum(II) compounds with mercury(II) carboxylates. X-ray, crystal and molecular structure of rac-[a-(m-MeCO2)-cf,de-(2-Me2NCH2C6H4)2PtHg(O2CMe)]

Abstract

The reactions of C~~-[(~-M~~NCo~btHain~edC fHrom~ )[P~tCP12~(S~Et2])2,a] n d [(2-MeJW6H4CH2)Li(TMEDA)] (TMEDA = tetramethylethylenediamine), and of cis-[( 2-Me2NCH2C6H4)2Pt1w1]i th Hg11(02CR)2( R = Me, i-Pr) yielded a novel type of cyclometalated Pt-Hg compound [(N-C)2(RCOJPtHg(02CR)] (N-C = 2-Me@C6H4CH2- and 2-Me$JCH2C6H4-). An X-ray crystallographic study defined the molecular structure of [(2-Me2NCH2C6H,)2(r-MeC02)PtHg(02TChMee )]. pertinent crystal data are as follows: orthorhombic, space group Pccn, Z = 8, a = 14.817 (8) A, b = 17.339 (9) A, c = 18.602 (11) A. The platinum center is six-coordinate with a Pt-Hg bond (2.513 (1) A) bridged by one acetato group: Pt-0, 2.15 (1) A; Hg-O’, 2.62 (1) A. The other acetato ligand is monodentate bonded to Hg: Hg-O,2.10 (1) A. The mercury atom and the two carbon ligands are mutually cis. A cis oxidative addition, involving a platinum-to-mercury-bonded intermediate, is proposed for the reaction mechanism. The geometry of the other compounds [(2-Me2NCH2C6H4)2(i- PrC02)PtHg(02C-i-Pr)] and [ (2-Me2NC6H4CH2),(RC02)PtHg(02(CRR )=] M e, i-Pr), as deduced from ‘H and I3C NMR spectra, is similar. Intramolecular exchange of the two carboxylato groups is not observed. Exchange of these carboxylato groups with free carboxylic acids occurs on different time scales. Reactions of ?~U~~-[(~-M~~NCHwi,thC ~H~)~P~I~] Hg”(O2CR), proceeded via an unstable Pt-Hg intermediate, which then eliminated Hgo to form [(2- Me2NCH2C6H4)2Pt(02CR)2a]s a mixture of two isomers. Reaction of ( [2,6-(Me2NCH2)2C6Hs]Pt11X(X) = Br, O,CR), containing a terdentate ligand, with Hg11(02CR), resulted in formation of the stable Pt-Hg-bonded compounds ([2,6- (Me2NCH2)2C6H3](RC02)PtHg(02C(XR )=X B)r , 02CR; R = Me, i-Pr). For these compounds a structure is proposed containing a five-coordinate Pt center and a carboxylato-bridged Pt-to-Hg donor bond. The structure of the compound with X = Br results from an exchange of the bromide atom and a carboxylato group between the platinum and mercury centers. Intramolecular carboxylato exchange is observed for which a mechanism, involving a six-coordinate Pt intermediate, is proposed. For the compound ( [2,6-(Me2NCH2)2C6H(3i]- PrC02)PtHgC12], prepared from ( [2,6-(Me2NCH2),C6H3]- Pt(02C-i-Pr)) and HgCl,, a structure with a carboxylato group bridging between Pt and HgC12 is proposed. The dynamic behavior of these compounds in solution is discussed