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The use of various diethynylarene ligands in the synthesis of some metal carbonyl linking clusters is established. New dimeric complexes of osmium [{(μ-CO)Os3(CO)9}2(μ3-η2-diyne)], ruthenium [{(μ-H)Ru3(CO)9}2(μ3-η2,η2-diyne)] or [{(μ-CO)Ru3(CO)9}2(μ3-η2-diyne)] and cobalt [{Co2(CO)6}2(η2-diyne)] (diyne = HC≡CArC≡CH, Ar = 2,7-fluorene, 2,7-fluoren-9-one, bithiazole or bithiophene) have been prepared in good yields from the reaction of [Os3(CO)10(NCMe)2], [Ru3(CO)12] or [Ru3(CO)10(NCMe)2] and [Co2(CO)8] with half an equivalent of the appropriate diethynylarene ligand, respectively. All these cluster compounds have been characterized by IR and 1H NMR spectroscopies and mass spectrometry. The molecular structures of three of them have been determined by X-ray crystallography. For the group 8 osmium and ruthenium analogues, the hexanuclear carbonyl clusters consist of two trinuclear metal cores with the exhibition of the μ3-(η2-||) bonding mode for the acetylene groups when [M3(CO)10(NCMe)2] (M = Ru, Os) was used and the μ3-η2,η2 bonding mode when [Ru3(CO)12] served as the starting cluster. The tetracobalt species possesses two Co2C2 cores adopting the pseudo-tetrahedral geometry having the alkyne bond lying perpendicular to the Co–Co vector in each core. Density functional theory was also used to study the electronic structures of selected molecules.

Reaction of (Ru2(CO)6(μ-PFu2)(μ- 1 , 2 -Fu)) (Fu = furyl) 1 with tri(2-furyl)phosphine under thermal conditions produces simple mono- and disubstitution products (Ru2(CO)5(PFu3)(μ-PFu2)(μ- 1 , 2 -Fu)) 2a and (Ru2(CO)4(PFu3)2(μ- PFu2)(μ- 1 , 2 -Fu)) 2b. Both complexes were fully characterized by spectroscopic and analytical methods and the molecu- lar structures of 2a and 2b were established by X-ray crystallography. The Ru Ru edge bridged by the μ- 1 , 2 -bound PFu2 fragment remains intact after the substitution reaction. The product yields of both complexes depend on the stoichiometry of the reactants. All of these new diruthenium complexes are electron precise with 34 cluster valence elec- trons. tion metals in low oxidation states (4). The pioneering work by Farina and co-workers showed the use of PFu3- derived palladium catalysts to be highly advantageous in the Stille cross-coupling reaction with significant rate ac- celerations being observed over traditional PPh3-based catalysts, presumably by virtue of its low electron-donating ability toward Pd(II) center (5). Since then, numerous re- searchers have sought to evaluate the performance of PFu3 in a wide variety of metal-catalyzed processes for the preparation of small molecules, complex natural products as well as polymers (3). In many cases, Stille coupling with the PFu3 ligand allows for milder reaction conditions and hence the attenuation of unwanted side reactions. How- ever, accurate prediction of whether this poor  -donating PFu3 ligand will lead to beneficial effects for a given proc- ess still remains elusive.

The difurylphosphido-bridged dinuclear complex [Ru2(CO)6(μ-PFu2)(μ-η1,η2-Fu)] (Fu = 2-furyl) 1 readily reacts with two equivalents of each of the terminal alkynes HC≡CR (R = Fc, p-C6H4Fc, p-C6H4NO2, Fc = Fe(η5-C5H5)(η5-C5H4)) by an interesting head-to-tail ynyl coupling with a furan group to form a series of phosphido-bridged diruthenium compounds containing a novel furyl-substituted C4 hydrocarbyl chain of stoichiometry [Ru2(CO)4(μ-PFu2){μ-η1,η1,η2,η3-RCC(H)C(R)C(H)Fu}] (R = Fc 2, p-C6H4Fc 3, p-C6H4NO2 4) in moderate to good yields. Reaction of 1 with an equimolar amount of HC≡CFc and HC≡C(p-C6H4NO2) afforded a pair of isomers of [Ru2(CO)4(μ-PFu2){μ-η1,η1,η2,η3-R1CC(H)C(R2)C(H)Fu}] (R1 = Fc, R2 = p-C6H4NO2 5a; R1 = p-C6H4NO2, R2 = Fc 5b) together with a small mixture of 4. X-ray crystal structures of 2, 3, 5a and 5b are reported. All of these new alkyne-derived dinuclear complexes are electron precise with 34 cluster valence electrons in which the μ-η1,η2-furyl ligand acts as a three-electron donor and the μ-phosphido Ru2 framework is retained in the products upon alkyne coupling reactions. The resulting organic fragment of each complex is coordinated to the Ru atoms via a π, a π-allyl and two σ bonds, and donates seven electrons to the metal core.

Thermal reaction of [Ru2(CO)6(μ-PFu2)(μ-η1,η2-Fu)] (Fu=2-furyl) with (9-anthracenyl)diphenylphosphine (AnPPh2) produces a novel diruthenium complex [Ru2(CO)5(μ-PFu2)(μ-η1,η1,η2-C14H8PPh2)] (1) in good yield whereas the corresponding reaction between [(μ-H)4Ru4(CO)12] and AnPPh2 gives [HRu(CO)3(PPh2C14H8)][(μ-H)4Ru4(CO)11(AnPPh2)] (2). Both compounds 1 and 2 were fully characterized by spectroscopic methods and their X-ray crystal structures were determined. For 1, initial coordination of the PPh2 functionality at the Ru atom is accompanied by cyclometalation of the anthracenyl ring to form a Ru–C σ bond together with concomitant formation of a π bond to the adjacent Ru center and loss of the furyl ligand. The formation of 2 involves the cleavage of two Ru–Ru bonds, and the making of a Ru–P bond, followed by orthometalation of the anthracenyl ring. The optical absorption and emission spectra of 1 were recorded and the results were correlated to the DFT calculations.

Tri(2-furyl)phosphine (PFu 3 ) reacts with [Ru 4 (μ-H) 4 (CO) 1 2 ] (1) in refluxing THF to give, apart from an isomeric pair of the substituton products [Ru 4 (μ-H)4(CO) 1 0 (PFu 3 ) 2 ] (2a and 2b), the μ-phosphido cluster [Ru 4 (μ-H) 2 (CO) 8 (PFu 3 ) 2 (μ-PFu 2 )(μ-η 1 ,η 2 -C 4 H 3 O)] (3) and a series of μ 3 - and μ 4 -phosphinidene clusters [Ru 4 (μ-H)2(CO) 1 2 - x (PFu 3 ) x (μ 3 -PFu)] (x = 0 (4), 2 (5), 3 (6)) and [Ru 4 (μ-H) 2 (CO) 9 (PFu 3 ) 2 (μ 4 -PFu)(μ 3 -η 1 ,η 1 ,η 2 -C 4 H 2 O)] (7). In this one-pot reaction, the excellent facility for PFu 3 to act as rich sources of furyl, furyne, phosphide (μ-PR 2 ), and phosphinidene (μ 3 -PR and μ 4 -PR) fragments on tetrametallic frameworks has been demonstrated. The single-crystal X-ray structures of all new molecules have been determined. The structure of 7 represents the first structurally characterized example of stable furyne-containing cluster complexes of ruthenium. The electrochemical behavior and molecular orbital calculations of these metallophosphorus clusters have been examined as a function of the coordination modes of the phosphorus-containing moieties.

Thermal reaction of [Ru2(CO)6(μ-PFu2)(μ-η1,η2-Fu)] (Fu = 2-furyl) (1) with bis(diphenylphosphanyl)methane (dppm), bis(diphenylphosphanyl)amine (dppam), or bis(diphenylphosphanyl)methylamine (dppma), produces the substitution products [Ru2(CO)4(μ-PFu2)(μ-η1,η2-Fu)(μ-L)] [2 (L = dppm), 3 (L = dppam), 4 (L = dppma)] in good yields. The Ru−Ru edge is bridged by the diphosphane in each case, while the μ-η1,η2-bound furyl fragment remains intact. When the reactions were carried out using bis(diphenylphosphanyl)ethane (dppe) or bis(diphenylphosphanyl)propane (dppp), the compounds [Ru2(CO)5(μ-PFu2)(μ-η1-C6H4PPh(CH2)nPPh2)] [5 (n = 2), 6 (n = 3)] were isolated as the thermodynamic products in which both P atoms chelate to one Ru centre to afford five- (for 5) and six-membered (for 6) ruthenacycles, accompanied by orthometallation of one of the phenyl rings of the phosphane ligand. Interestingly, elimination of the coordinated furyl moiety occurs during the formation of 5 and 6. Upon reaction with bis(diphenylphosphanyl)butane (dppb), bis(diphenylphosphanyl)pentane (dpppe), or bis(diphenylphosphanyl)ferrocene (dppf), cyclometallation is not favoured in each case. Instead, [{Ru2(CO)5(μ-PFu2)(μ-η1,η2-Fu)}2(L)] [7a (L = dppb), 8a (L = dpppe), 9a (L = dppf)] and polymeric [Ru2(CO)4(μ-PFu2)(μ-η1,η2-Fu)(L)]n [7b (L = dppb), 8b (L = dpppe), 9b (L = dppf)] were obtained with the product yield depending on the stoichiometry of the reactants. All these new diruthenium complexes are electron-precise with 34 cluster valence electrons. (© Wiley-VCH Verlag GmbH, 69451 Weinheim, Germany, 2002)

Treatment of [Os3(CO)10(NCMe)2] with platinum bis(alkynyl) complexes cis-[Pt(C≡CPh)2(L)] [L = 4,4′-dimethyl-2,2′-bipyridine (Me2bipy), 4,4′-bis(tert-butyl)-2,2′-bipyridine (tBu2bipy)] at room temperature readily affords the novel, spiked-triangular heterometallic cluster complexes [Os3Pt(CO)9(μ4-η2-C≡CPh)(η1-C≡CPh)(L)] (L = Me2bipy 1, tBu2bipy 2) in moderate yields. X-ray analysis of both complexes reveals that one alkynyl moiety is coordinated to the metal atoms in a μ4-η2(||) mode, accompanied by a concomitant transfer of an η1-C≡CPh group from the platinum centre to the osmium atom to give a metal framework with an osmium atom apically bonded to an Os2Pt triangle.

Thermal reaction of [Ru3(CO)12] with tri(2-furyl)phosphine affords the dinuclear phosphido-bridged complex [Ru2(CO)6{μ-P(C(CH)3O)2}(μ-η1,η2-C(CH)3O)] 1a in good yield via cleavage of Ru–Ru and P–C(furyl) bonds in the starting compounds and a small amount of the disubstitution product [Ru3(CO)10{P(C(CH)3O)3}2] 1b. The X-ray structural analysis of 1a shows that it contains a dissociated furyl fragment bonded to the Ru2 unit in a μ-η1,η2 coordination mode through one σ and one π bond. This represents the first structurally characterised example of such a furyl-bonded dinuclear organometallic complex. Complex 1a readily reacts with two equivalents of terminal alkynes HCCR [R = Ph, p-C6H4Me, p-C6H4NO2, (C4H2S)CCH or (C4H2S)2CCH] by an interesting head-to-tail ynyl coupling with a furan group to form a series of phosphido-bridged diruthenium compounds containing a novel furyl-substituted C4 hydrocarbyl chain of stoichiometry [Ru2(CO)4{μ-P(C(CH)3O)2}{μ-η1,η1,η2,η3-RCC(H)C(R)C(H)C(CH)3O}] [R = Ph 2, p-C6H4Me 3, p-C6H4NO24, (C4H2S)CCH 5 or (C4H2S)2CCH 6] in moderate to good yields, all of which have been characterised by spectroscopic and crystallographic methods. Assignments of the proton NMR spectra have been made with the aid of a 2-D 1H–1H COSY technique. On reaction with the thienyl-linked diyne ligands, only one free CCH group is involved in the coupling sequence while the other terminal alkyne functionality remains intact. All these new dinuclear complexes are electron precise with 34 cluster valence electrons.