CARBENE AND CARBYNE COMPLEXES OF TECHNETI UM AND RHENIUM - SYNTHESIS,STRUCTURE AND REACTIONS

Synthesis, structure and reactions of technetium and rhenium complexes bearing metal-carbon multiple bonds are reported. Addition of LiPh to CpM(CO)(3) (1a: M = Tc; Ib: M = Re) (Cp* = eta(5)-C(5)Me(5)) in Et(2 )O yields the acyl complexes Li[Cp(CO)(2)MC(O)Ph]. Et(2)O (2a: M = Tc ; 2b: M = Re). These are converted with Et(3)OBF(4) into the carbene c omplexes Cp(CO)(2)M = C(OEt)Ph (3a, 3b. Reaction of 3a and 3b with BC l3 affords the carbyne complexes [Cp(CO)(2)M=CPh]BCl4 (4a, 4b) in hig h yield. The acyl complex 2b can be directly converted into the carbyn e complex [Cp(CO)(2)Re=CPh]Br (5b), when it is treated with oxalyl br omide. Nucleophiles add at the carbyne-carbon atoms of 4a and 4b, as d emonstrated by the reaction with NaOCy (Cy = cyclohexyl) to afford the carbene complexes Cp(CO)(2)M = C(OCy)Ph (6a, 6b). Similarly, reactio n of P(OMe)(3) with [Cp(CO)(2)Re=CPh]Cl (5b'), the latter being gener ated in situ from 2b and oxalyl chloride, gives the ylide complex {CP (CO)(2)Re= C[P(OMe)(3)]Ph}Cl(7b'). In comparison, addition of P(OMe)(3 ) to [Cp(CO)(2)Tc=CPh]Cl (5a'), generated in situ from 2a and oxalyl chloride, induces a carbyne-carbonyl coupling reaction resulting in th e formation of the ketenyl complex (Cp(CO)[P(OMe)(3)]TcC(CO)Ph)Cl (7a '). Thermolysis of the compounds 2a, 2b, 4a, 4b and 7b' has been studi ed in vacuo and the products of decomposition identified by IR spectro scopy. The solid-state structure of the carbene complexes 3a and 3b wa s determined by single crystal X-ray diffraction studies. Both compoun ds crystallize in the monoclinic space group P2(1)/n with very similar unit cell data. Striking feature of the isostructural carbene complex es is the nearly perpendicular orientation of the carbene ligand relat ive to the Cp ring.