Reactions of [H 2 Os 3 (CO) 10 ] with the substituted diynes R-C 5), and {µ-η 1 :η 1 -CH 3 CCdC-C(H)dC(H)-NPh} (6), which have been characterized by single-crystal X-ray diffraction analyses as well as by various spectroscopic methods. In clusters 4-6, the starting diynes 1-3 have been rearranged to form substituted pyrrolyl rings which bridge two osmium atoms in η 1 :η 2 -(4, 5) or η 1 :η 1 -(6) coordination modes depending on the nature of substituents in 1-3. A possible reaction pathway for the diyne cyclization reactions that yield 4-6 involves initial transfer of a hydride onto a coordinated diyne followed by a series of 1,3-shifts and subsequent nucleophilic attack of the nitrogen on the third carbon atom of the diyne system to afford the five-membered pyrrolyl ring. Cluster 6 and its previously characterized furanyl analogue [HOs 3 (CO) 10 {µ-η 1 :η 1 -(OCH-CHCC)-C-CH 3 )}] (7) undergo facile thermal transformation accompanied by the loss of a CO ligand to give the clusters [HOs 3 (CO) 9 {µ 3 ,η 3 -CH 3 CCdC-C(H)dC(H)-NPh}] (8) and [HOs 3 (CO) 9 {µ 3 ,η 3 -(OCHdCHCdCCCH 3 )}] (9). In both 8 and 9, single-crystal X-ray analysis revealed the presence of pentagonal pyramid cluster cores containing three osmium and three carbon atoms.

Reactions of [H2Os3(CO)10] with a series of diynes, RC2C2R‘ (1:  R = Ph, R‘ = CH2OH; 2:  R = Ph, R‘ = C(O)Ph; 3:  R = R‘ = C(OH)Me2), have been studied. It was found that upon coordination to the triosmium cluster, the nucleophilic oxygens of the R‘ substituents of 1 and 2 take part in intramolecular cyclization reactions to give [HOs3(CO)10{μ-η1:η2-PhCH2(CCH−CCH−O)}] (5) and [HOs3(CO)10{μ-η1:η1-Ph(CCH−CC−O)CPh}] (6), respectively, both of which contain furan rings coordinated to the cluster core. On heating of the latter compound, the furan moiety remains intact, but a carbonyl group dissociates from the cluster, leading to the formation of [HOs3(CO)9(μ3-η1:η3:η1-Ph(CCH−CC−O)CPh)] (7) with a closed “C3Os3” pentagonal pyramidal structure. Reaction of [H2Os3(CO)10] with 3 does not lead to cyclization of the diyne; instead, the clusters [Os3(CO)10{μ3-η2-(RCHCH−C2R)}] (8) and [Os3(CO)10{μ3-η2-(RC2C2R)}] (9) are formed. Deuterium labeling of the starting compounds has been used in the reaction of [H2Os3(CO)10] with HOCH2C2C2CH2OH in order to investigate possible mechanisms of the cyclization reaction. The crystal and molecular structures of clusters 5, 7, and 9 are presented.

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Reactions between unsaturated [H(2)Os(3)(CO)(9)(PR(3))] clusters (PR(3)= PPh(3), P(4-CF(3)-C(6)H(4))(3), PEt(3)) and 2,4-hexadiyne-1,6-diol have been studied. It was found that the diyne ligand easily reacts with all these complexes to give [HOs(3)(CO)8(PR3)-[mu3, eta1:eta3:eta1)-(CH(3)-C-C=CH-CH=C-O)]] complexes (V, VI and VII, respectively) containing the "Os3C3" pentagonal pyramid cluster framework. This structural pattern is formed through the diyne cyclization, dissociation of a CO ligand and eventual coordination of the cyclized organic moiety to the osmium triangle in the [mu3, eta1:eta3:eta1) manner. In the case of the PEt(3) substituted cluster the second hydride transfer onto the organic fragment occurs to afford the nonhydride [Os(3)(CO)(8)(PR3)[mu3), eta1:eta2:eta1)-(CH(3)-CH-C=CH-CH=C-O)]] cluster, VIII, containing distorted pentagonal pyramid framework with a broken Os-C bond. Heating V, VI of VII and in hexane solutions results in formation of the regioisomers (Va, VIa and VIIa) with the phosphine ligand located at adjacent osmium atoms across the Os-Os bond bridged by the coordinated organic fragment. The most probable mechanism of the isomerization includes reversible phosphine migration between these metal centres. Solid-state structure of V, Va, VI, VIIa and VIII have been established by single crystal X-ray diffraction. A general mechanistic scheme for the diyne ligand cyclization and cluster framework transformations is suggested and discussed.

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