The Allenylidene Complex [Ru(η5-C5H5)(CCCPh2)(CO)(PiPr3)]BF4 as a Precursor of Novel Pyrido[1,2-a]pyrimidinyl and 1,3-Thiazinyl Complexes

The allenylidene complex [Ru(η 5 -C 5 H 5 )(C C CPh 2 )(CO)(P i Pr 3 )]BF 4 ( 1 ) reacts with 2-aminopyridine to give a mixture of the complexes [Ru(η 5 -C 5 H 5 ){2,2-diphenyl-2 H -pyridinium[1,2- a ]pyrimidin-4-yl}(CO)(P i Pr 3 )]BF 4 ( 2 ) and ( 3 ). The molar ratio of the isomers in the mixture depends on the reaction temperature. At temperatures lower than −30 °C, isomer 2 is the main reaction product, while at 0 °C an inverse relationship is observed. The structure of 2 has been determined by an X-ray investigation, revealing a Ru−C(bicycle) distance of 2.08(1) Å. Treatment of 2 with sodium methoxide results in the deprotonation of the NH group of the heterocycle to give the pyrido[1,2- a ]pyrimidinyl derivative Ru(η 5 -C 5 H 5 ){2,2-diphenyl-2 H -pyrido[1,2- a ]pyrimidin-4-yl}(CO)(P i Pr 3 ) ( 4 ), which has been also characterized by an X-ray diffraction analysis. In this case, the study reveals a Ru−C(bicycle) distance of 2.097(5) Å. The deprotonation of 2 is reversible. Thus, the addition of HBF 4 ·OEt 2 to dichloromethane solutions of 4 regenerates 2 . Similarly, the treatment of 4 with methyl trifluoromethanesulfonate affords [Ru(η 5 -C 5 H 5 ){1-methyl-2,2-diphenyl-2 H -pyridinium[1,2- a ]pyrimidin-4-yl}(CO)(P i Pr 3 )]CF 3 SO 3 ( 5 ). Complex 1 also reacts with thioisonicotinamide. The reaction yields [Ru(η 5 -C 5 H 5 ){4,4-diphenyl-2-( p -pyridinyl)-4 H -1,3-thiazinium-6−yl}(CO)(P i Pr 3 )]BF 4 ( 6 ), which in the presence of sodium methoxide affords Ru(η 5 -C 5 H 5 ){4,4-diphenyl-2-( p -pyridinyl)-4 H -1,3-thiazin-6-yl}(CO)(P i Pr 3 ) ( 7 ). The structure of 7 has been determined by an X-ray investigation, revealing a Ru−C(cycle) distance of 2.067(4) Å. The deprotonation of 6 is also reversible. Thus, the addition of HBF 4 ·OEt 2 to dichloromethane solutions of 7 regenerates 6 . Similarly, treatment of 7 with methyl trifluoromethanesulfonate gives [Ru(η 5 -C 5 H 5 ){3-methyl-4,4-diphenyl-2-( p -pyridinyl)-4 H -1,3-thiazinium-6-yl}(CO)(P i Pr 3 )]CF 3 SO 3 ( 8 ).