Decarbonylation of phenylacetic acids by high valent transition metal halides

Triphenylacetic acid underwent unusual decarbonylation when allowed to react with a series of halides of group 4-6 metals in their highest oxidation state, in dichloromethane at ambient temperature. Thus, the reaction of CPh 3 COOH with MoCl 5 , in 1:1 molar ratio, afforded the trityl salt [CPh 3 ][MoOCl 4 ], 1, in 79% yield, while the 1:2 reaction of CPh 3 COOH with NbF 5 afforded [CPh 3 ][NbF 6 ], 2, in 70% yield, NbOF 3 being the metal co-product. CPh 3 COOH reacted with NbCl 5 , TiF 4 and WOCl 4 to give mixtures of compounds, however the cation [CPh 3 ] + was NMR identified in each case. [CPh 3 ][NbCl 6 ], 3, was isolated from NbCl 5 and CPh 3 COCl, prior to being generated from CPh 3 COOH and PCl 5 . The reaction of CPh 3 COOH with TiCl 4 was non-selective, and the salt [CPh 3 ][Ti 2 Cl 8 (μ-κ 2 -O 2 CCPh 3 )], 4, was obtained in 18% yield. The decarbonylation reactions of CMePh 2 COCl and CMe 2 PhCOCl by means of NbCl 5 led to the indanes 5a-b, which were isolated in 79-97% yields after hydrolysis of the mixtures and subsequent alumina filtration of the organic phases. The reactions of CH(Ph) 2 COOH with NbCl 5 and WCl 6 afforded NbCl 4 (OOCCHPh 2 ), 6, and CHPh 2 COCl, respectively, as the prevalent species. CPh 2 (CH 2 CH 2 Br)COOH did not undergo CO release when allowed to interact with WCl 6 , instead selective intramolecular condensation to C(Ph) 2 C(O)OCH 2 CH 2 , 7, occurred. MeCCCOOH underwent hydrochlorination by WCl 6 to give MeC(Cl)CHCOOH, 8, in 72% yield. All the products were fully characterized by elemental analysis, IR and multinuclear NMR spectroscopy. In addition, the solid state structures of 1, 2, 4, 7, and 8 were elucidated by X-ray diffraction.