SYNTHESIS OF HETEROCYCLIC-SYSTEMS BY ACTIVATION OF ISOCYANIDE, CARBONYL, TRIFLUOROMETHYL AND NITRILE LIGANDS IN PLATINUM(II) AND PALLADIUM(II) COMPLEXES

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 HOCH2CH2X/base (X = Cl, Br; base = n-BuLi) to afford five-membered cyclic aminooxycarbenes of the general formula Pt = CN(R)CH2CH2O (R = alkyl, aryl) (type I structure). The corresponding reactions with Pd(II) isocyanides lead to Pd(0) species. Similar reactions of Pd(II)- and Pt(II)-metal bound isocyanides with NH2CH2CH2Br lead to five-membered cyclic diaminocarbenes of the general formula M = CN(R)CH2CH2N(H) (type I structure). Cyclic five-membered diamino-, aminothio- and aminooxycarbenes of the general type M = CN(R)CH2CH2X (X = NH, S, O) (type I structure) are obtained from metal coordinated RNC ligands by reaction with the three-membered heterocycles YCH2CH2, (Y = NH, aziridine; S, thiirane; O, oxirane), respectively. Among the four-membered heterocycles YCH2CH2CH2 (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-(BF4-R3P+-CH2)C6H4NC (R = alkyl, aryl) react with NEt3 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 = COCH2CH2N(H) (type I structure). The C-F bonds alpha to Pt in trans-L2PtX(CF3) (X = H, L = PPh3; X = Cl, L = PMe2Ph) are susceptible to electrophilic attack. The reaction with HBF4 leads to the formation of the highly reactive difluorocarbene intermediate Pt = CF2+, which reacts with diols and thiols to give five- and six-membered heterocycles of the type Pt = CX(CH2)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-Cl2Pt(NCR)2 react with HOCH2CH2Cl/base or oxirane/Cl- to afford N-coordinated oxazolines Pt-NC(R)OCH2CH2 (type IV structure). Mechanistic and structural aspects as well as some significant reactions and electrochemical behaviour of the metal-coordinated heterocycles are reported.