The cyclohexadienyl complexes [Mn(q5-C,H,R1)(CO),] 1 (R' = exo-H, M e or C,H,Me-4) react with LiR2 (R2 = M e or Ph) to give acylmetalates [Li(OEt,)] [Mn(7\5-C,H,R1)(CO),{C(0)R2}] 2. Complex 2 ( R1 = Me, R2 = Ph) has been characterised by an X-ray crystallographic study: orthorhombic, space group P212121, a = 9.1 13(2), b = 14.491 (8), c = 32.803(9) A, R = 0.064 for 1 4 5 8 independent reflections. Protonation of 2 with HBF,*Et20 induces an aryl-or alkyl-group transfer t o the endo face of the cyclohexadienyl ring yielding t h e new agostic cyclohexenyl complexes [Mn(q3:CHC6H,R1R2) (CO),] 3. The cyclohexenyl ligands can be decomplexed from the metal via treatment of 3 with 1,2-bis-(dipheny1phosphino)ethane (dppe) in tetrahydrofuran to afford mixtures of substituted cyclohexa-l,3dienes and [MnH(CO),(dppe)]. The acylmetalates 2 react with [NO] [BF,] at -78 "C to give [Mn(q5-C,H,R1) (CO) (NO){C(O) R2}] which decompose at room temperature to form the trans-disubstituted acylcyclohexadienes C,H,R1[C(0)R2]. Reaction of 2 with electrophiles SiMe,CI, [Me,O] [BF,] or [Et,O] [BF,] results in 0 alkylation and formation of stable carbene complexes [Mn(q5-C6H,R1)(CO),-{C(OE)R2}] ( E = SiMe,, M e or Et).
