Preparation and reactions of some orthomanganated ketones, amides and aldehydes
η²-(1-acetyl-2-indolyl)tetracarbonylmanganese (7, R=CH₃) and η²-(2-N,N- dimethylamidophenyl)tetracarbonylmanganese (13), the first examples of orthomanganated amides, have been synthesized by reaction of N-acetylindole and N,N-dimethylbenzamide respectively with PhCH₂Mn(CO)₅. 7 (R=CH₃) was identified by X-ray crystallography. Preparation of the N-benzoyl- (7, R=Ph) analogue highlights a preference for metalation at the 5-membered indolyl ring, rather than the benzoyl ring. The N-benzoylpyrrole analogue of 7, η²-(1-benzoyl-2-pyrrolyl)tetracarbonylmanganese (4) was also prepared. Orthomanganated N,N-dimethylbenzamide (13) showed only oxygen donation to manganese, despite the presence of a possible nitrogen donor. N,N-diethyl and N,N-pyrrolidinyl analogues of 13 behaved similarly. [diagram] (7) [diagram] (13) η²-(2-formyl-5-dimethylaminophenyl)tetracarbonylmanganese (21) and its 5-methoxy analogue were prepared similarly and are the first examples of orthomanganated aldehydes. 2-thiophenecarboxaldehyde and 3-thiophenecarboxaldehyde gave analogous 3-metalated and 2-metalated aldehyde products. Two new dimetalated arenes, η²,η²-(2,4-diacetylphenyl)bis-1,5- (tetracarbonyl)manganese (25) and η²,η²-(2,5-diacetylphenyl)bis-1,4-(tetracarbonyl)manganese (27), have been identified, in the former case by crystal structure analysis. The first examples of coupling reactions of orthomanganated carbonyl compounds with alkynes are reported that do not require a palladium(II) catalyst: η²-(2-acetylphenyl)tetracarbonylmanganese (39) was treated with diphenylacetylene to give in good yield 1-methyl-2,3-diphenylinden-1-ol (40), the structure of which was determined crystallographically. Acetylene, 4-octyne and bis(trimethylsilyl)-acetylene reacted similarly. For indenols arising from coupling with the unsymmetric alkynes phenylacetylene and trimethylsilylacetylene, the alkyne substituent occupied the 2-position in the final product. A possible mechanism for the couplings is discussed. [Diagram] (40) Coupling of diphenylacetylene was effected with three other types of substrate; η²-(2-N,N-dimethylamidophenyl)-tetracarbonylmanganese (13) gave 2,3-diphenylindenone, η²-(2- carboxymethyl-4,5,6-trimethoxyphenyl)tetracarbonylmanganese (51) gave 2,3-diphenyl-5-dimethylaminoindenone and η²-(2-formyl-5-dimethylaminophenyl)tetracarbonylmanganese (21) gave rise to 2,3-diphenyl-4,5,6-trimethoxyindenone. Coupling of amide (13) with excess acetylene, however, gave a cyclohexadienyl-Mn(CO)₃ compound (50). [Diagram] (50) η²-(1-acetyl-2-indolyl)tetracarbonylmanganese (7) coupled with dimethyl acetylenedicarboxylate to afford a tricyclic nucleus, that of dimethyl 1-methyl-1-hydroxypyrrolo[l,2a]indole-2,3-dicarboxylate (56). The product has potential applications in the synthesis of mitomycin-based anti-tumour agents. Its crystal structure is reported and is of interest as a rare example of a stable carbinolamine. Possible reaction pathways to the variety of product types are considered throughout. [Diagram] (56) Some preliminary studies into electrophilic substitutions of (arene)M(CO)₃ (M= Cr, Mn) complexes were conducted. Despite an apparent lack of success in this area, the experimental procedures are recorded.
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