Regioselective ortho ‐Metallation of 2‐Diphenylphosphanylpyridine and (2‐(2‐Diphenylphosphanyl)phenyl)‐1‐3‐dioxalane with Methyltetrakis(trimethylphosphane)cobalt(I)

Co(CH 3 )(PMe 3 ) 4 forms 100 % regioselectively with (2‐(2‐diphenylphosphanyl)phenyl)‐1,3‐dioxalane and 2‐diphenylphosphanyl‐pyridine, by elimination of methane, the four‐membered metallacycles Co{(C 3 O 2 HC 6 H 3 )P(C 6 H 5 ) 2 }(PMe 3 ) 3 ( 1 ) and Co{(CNC 4 H 3 )P(C 6 H 5 ) 2 }(PMe 3 ) 3 ( 4 ). The regioselectivity is independent of the steric requirement of the ortho substituent in the 2‐diphenylphosphanylaryl‐ligands. Oxidative addition with iodomethane transforms 1 and 4 into octahedral, diamagnetic low‐spin d 6 complexes Co(CH 3 )I‐{(C 3 O 2 HC 6 H 3 )P(C 6 H 5 ) 2 }(PMe 3 ) 2 ( 2 ) and Co(CH 3 )I‐{(CNC 4 H 3 )P(C 6 H 5 ) 2 }(PMe 3 ) 2 ( 5 ). Under an atmosphere of carbon monoxide, insertion into the Co‐C bond results in ring expansion by forming the new assembled phosphanylbenzoyl complexes Co{(C 4 O 3 HC 6 H 3 )‐P(C 6 H 5 ) 2 }CO(PMe 3 ) 2 ( 3 ) and Co{(OCNC 4 H 3 )P(C 6 H 5 ) 2 }CO(PMe 3 ) 2 ( 6 ). The three different types of cobaltacycles are supported by X‐ray diffraction of 1 , 3 , 5 and 6 .