Synthesis and reactions of some orthomanganated complexes

Abstract

New orthomanganated indoles of the types shown in Figure 1 have been prepared, including two new examples of orthomanganated aldehydes which are relatively rare. The first crystal structure determination of an orthomanganated aldehyde was carried out on η²-(1-methyl-3-formyl-2-indolyl)tetracarbonylmanganese (11). Figure 1 Solvent effects on the thermally induced coupling reactions of η²-(2- acetylphenyl)tetracarbonylmanganese (9) and η²-(1-acetyl-2 indolyl)tetracarbonylmanganese (4) with a range of alkynes were shown to influence the course of reaction markedly but unpredictably. Of special interest was the reactions of (4) with dimethyl acetylenedicarboxylate which afforded the tricyclic carbinolamine (17) (Figure 2). Reactions of other orthomanganated indole derivatives with various alkynes are also reported. For example, a complex (21) (Figure 2) arising from the triple-insertion of ethyne was characterised by a single X-ray crystal structure determination, as a η³-allyl species that could be converted to a η⁵-C₅H₅ complex on heating. Figure 2 A new class of orthomanganated compound (Figure 3) has been prepared from the reaction of PhCH₂Mn(CO)₅ with triphenylphosphine chalcogens (Figure 3). These are the first reported examples of orthometalated tertiary phosphine chalcogenide metal complexes. Single crystal X-ray structure determinations of the examples with X=S (31) and Se (32) were determined. Figure 3 Cis-PhCH₂Mn(CO)₄PPh₃ (34) and [Mn(CO)₄(μ-SeCH₂Ph)]₂ (33) were also isolated from the orthomanganation reaction of Ph₃P=Se, with the latter being identified by a crystal structure determination. The thermally induced coupling reactions of orthomanganated Ph₃P=S (31) with the alkenes methyl vinyl ketone, methyl acrylate and acrylonitrile gave mainly arylalkane products (Figure 4) in moderate yields. Similar alkyne-coupling reactions of orthomanganated Ph₃P=S (31) were explored. Reaction with dimethyl acetylenedicarboxylate yielded (39) (whose crystal structure is reported) (Figure 4), and a doubly inserted alkyne complex was tentatively identified. Figure 4 However, the insertion of alkynes into the Mn-Cₐᵣᵧₗ bond of (31) was not general, as methyl propiolate was the only other alkyne to undergo insertion. Sulfur dioxide inserts efficiently into the Mn-C ₐᵣᵧₗ bond of orthomanganated Ph₃P=S (31) and Ph₃P=Se (32), to give the corresponding S-sulfinato complexes which contain novel metallocyclic rings (Figure 5). Figure 5 The X-ray crystal structure of the example with X=Se (45) was determined: it has a six-membered metallocycle ring incorporating five different elements. Reactions of other cyclomanganated species with SO₂ were found to be less straightforward. Preliminary investigations into the reactions Ph-N=S=O and Ph-N=C=O with orthomanganated Ph₃P=S are also described. The crystal structure of the phosphite substituted complex (40) (Figure 6) was determined, and its reactivity towards SO₂ and an alkyne was compared with that of the unsubstituted precursor. Figure 6