Synthesis of heterocyclic systems by activation of isocyanide, carbonyl, trifluoromethyl and nitrile ligands in platinum(II) and palladium(II) complexes

Abstract

Pd(II)- and Pt(II)-coordinated isocyanide, carbonyl and trifluoromethyl ligands are converted to heterocyclic carbenes (type I–III structures), while nitrile ligands are converted to oxazolines (type IV/structure) using different synthetic strategies. Thus, RNC ligands in Pt(II) complexes react with HOCH 2CH 2X/base (XCl, Br; base=nBuLi) to afford five-membered cyclic aminooxycarbenes of the general formula Pt= CN(R)CH 2CH 2O (R=alkyl, aryl) (type I structure). The corresponding reactions with Pd(II) isocyanides lead to Pd(O) species. Similar reactions of Pd(II)- and Pt(II)-metal bound isocyanides with NH 2CH 2CH 2Br lead to five-membered cyclic diaminocarbenes of the general formula M CN(R)CH 2CH 2N(H) (type I structure). Cyclic five-membered diamino-, aminothio- and aminooxycarbenes of the general type M CN(R)CH 2CH 2X (XNH, S, O) (type I structure) are obtained from metal coordinated RNC ligands by reaction with the three-membered heterocycles YCH 2CH 2 (YNH, aziridine; S, thiirane; O, oxirane), respectively. Among the four-membered heterocycles YCH 2CH 2CH 2 (YNH, S, O) only azetidine was found to react with some Pd(II)- and Pt(II)-isocyanides to afford acyclic diaminocarbenes. Pt(II)-coordinated phosphonium-functionalized isocyanides of the type o-(BF 4, −R 3P +-CH 2)C 6H 4NC (R=alkyl, aryl) react with NEt 3 to give indole derivatives (type II structure). When R is a benzyl group, the reaction with KOH produces heterometallacycles (type III structure). Pt(II)-bound CO ligands are converted to cyclic aminooxycarbenes of the type Pt COCH 2CH 2N (H) (type I structure). The CF bonds α to Pt in trans-L 2PtX(CF 3) (XH, LPPh 3; XCl, LPMe 2 2Ph) are susceptible to electrophilic attack. The reaction with HBF 4, leads to the formation of the highly reactive difluorocarbene intermediate PtCF 2 +, which reacts with diols and thiols to give five- and six-membered heterocycles of the type Pt CX(CH 2) nX ( n=2, XO, S; n=3, XO) (type I structure). Nitrile ligands coordinated to Pt(II) in complexes of the type cis- and trans-Cl 2Pt(NCR) 2 react with HOCH 2CH 2Cl/base or oxirane/Cl - to afford N-coordinated oxazolines Pt NC(R)OCH 2CH 2 (type IV structure). Mechanistic and structural aspects as well as some significant reactions and electrochemical behaviour of the metal-coordinated heterocycles are reported. ▪