Cage Substitution Reactions of Monocarbollide Carbonyl Complexes of Iron: Generation of Iminium Groups at a Boron Vertex

Treatment of [N(PPh 3 ) 2 ][Fe(CO) 2 (L)( η 5 -7-CB 10 H 11 )] (L = SMe 2, PPh 3 ) in SMe 2 or O(CH 2 ) 4 with H 2 SO 4 yields the neutral charge-compensated complexes [Fe(CO) 2 (L)( η 5 -9-L‘-7-CB 10 H 10 )] (L = SMe 2, L‘ = SMe 2 ( 2 ), O(CH 2 ) 4 ( 3 ); L = PPh 3, L‘ = SMe 2 ( 4 ), O(CH 2 ) 4 ( 5 )). An X-ray crystallographic study of 2 established that one of the exopolyhedral SMe 2 groups is bonded to a boron in a β -site with respect to the carbon in the ring coordinated to the iron atom. In contrast with these results, the salts [N(PPh 3 ) 2 ][Fe(CO) 2 (L)( η 5 -7-CB 10 H 11 )] (L = CO, PPh 3, CNBu t ) treated with NCMe and CF 3 SO 3 Me afford complexes [Fe(CO) 2 (L)( η 5 -9-{( E )-N(Me) C(H)Me}-7-CB 10 H 10 )] (L = CO ( 8 ), PPh 3 ( 9 ), CNBu t ( 10 )). An X-ray diffraction study on 8 established that the iminium group was attached to a β -B atom of the CB 4 iron-bonded ring. Compound 8 is readily hydrolyzed in the presence of a base catalyst affording [Fe(CO) 3 ( η 5 -9-NH 2 Me-7-CB 10 H 10 )] ( 12 ), and with [Na][BH 3 CN] yields [Fe(CO) 3 ( η 5 -9-{NH(Me)Et}-7-CB 10 H 10 )] ( 13 ), the structure of which was determined by X-ray diffraction. The reaction between [N(PPh 3 ) 2 ][Fe(CO) 3 ( η 5 -7-CB 10 H 11 )] and Bu t C⋮CH gives [N(PPh 3 ) 2 ][Fe(CO) 3 ( η 2: η 5 -8-{( E )-C(H) C(H)Bu t }-7-CB 10 H 10 )] ( 14 ), which with NCMe in CF 3 SO 3 Me affords [Fe(CO) 2 ( η 2: η 5 -8-{( E )-C(H) C(H)Bu t }-10-{( E )-N(Me) C(H)Me}-7-CB 10 H 9 )] ( 16 ). The site of attachment of the exopolyhedral iminium and tert -butylvinyl substituents to the cage was established by X-ray diffraction.