Hydroxyalkynyl complexes

Extending the carbon chain of vinylidenes by one or three carbons provides linear cumulenated ligands, LwM=(C=C)w=CR2 (n = 1,2). These compounds have been studied in considerable detail, especially allenyl-idenes (n = 1) and arise in most cases from the rearrangement and dehydration (often spontaneous) of hydroxyalkyl alkynes or diynes (Figure 5.51). Various intermediates (Figure 4.18) may be envisaged (and occasionally isolated) which are related by elimination/addition of H+ or hydroxide, e.g. y-hydroxyalkynyl complexes have been isolated and subsequently dehydroxylated with Lewis or Bronsted acids. 

Treatment of 133 at room temperature with a suspension containing 1 equiv of TlPFg and 1.52 equiv of l,l,-diphenyl-2-propyn-l-ol produces the activation of the Os-Cl of the starting complex, and the oxidative addition of the H-C(sp) bond of the alkynol to the resulting unsaturated metallic fragment [Os(r]5-C5H5)(P Pr3)2]". As a result the hydroxyalkynyl-osmium(IV) derivative [OsH(ri5-C5H5) C=C(OH)Ph2 (P Pr3)2]PF6 (154) is obtained (Scheme 40) [59]. 

Ph=GH2)Gp (PEt3)2][BPh4] and [OsH(G=GGPh=GH2)Gp(PPp3)2][PF6] are also known. They have been obtained by dehydration of the methyl-substituted 3-hydroxyalkynyl ligand in complexes [RuH G=GG(OH)-MePh Cp (PEt3)2][BPh4] and [OsH feCC(OH)MePh Cp(PPr 3)2][PF6], respectively.Deprotonation of the optically active indenyl-ruthenium(ii) allenylidene 138 with KOBu to yield 139 has also been reported (see Equation (9)). 

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