Synthesis of cobalt-containing monodentate phosphine ligand and application toward Suzuki cross-coupling reactions

A bulky, dicobalt complexed, mono-dentate phosphine, [(μ-PPh₂CH₂PPh₂)Co₂(CO)₄](μ,η-PhCCPCy₂) (4), was prepared from the reactions of the bis(diphenylphosphino)methylene (dppm)-bridged dicobalt complex Co₂(CO)₆(μ-Ph₂PCH₂PPh₂) (2) with PhCCPCy₂ (3). Combination of 4 and Pd(OAc)₂ (1:1) gave an active catalyst for the palladium-catalyzed Suzuki coupling of aryl bromides with phenylboronic acid; the catalytic reactions can be performed even under low catalyst loadings (0.1-0.001 mol% 4/Pd(OAc)₂). Compound 4 has been proved to be an authentic and effective mono-dentate phosphine ligand. Crucial factors such as 4/Pd(OAc)₂ ratio, base being used, solvent volume, temperature, and electronic variation of the aryl bromides in reactions were also investigated and results are reported.     

Reaction of the heterometallic cluster Os3Ru(μ-H)2(CO)13 with diphenylphosphine: phosphido-bridged tetrahedral and butterfly clusters

TMNO-activated reaction of the heteronuclear cluster Os₃Ru(μ-H)₂(CO)₁₃ (1) with diphenylphosphine afforded the novel phosphido-bridged clusters Os₃Ru(μ-PPh₂)(μ-H)₃(CO)₁₁ (2), Os₃Ru(μ-PPh₂)₂(μ-H)₂(CO)₁₀ (3), Os₃Ru(μ-PPh₂)₂(μ-H)₄(CO)₉ (4), and Os₃Ru(μ-PPh₂)(μ-H)₃(CO)₁₁(PPh₂H) (5). The formation of 2-5 proceeded via P-H bond cleavage in the adduct Os₃Ru(μ-H)₂(CO)₁₂(PPh₂H) (6). Reaction of 2 with PPh₃ afforded the adduct Os₃Ru(μ-PPh₂)(μ-H)₃(CO)₁₁(PPh₃) (7) and the substituted derivative Os₃Ru(μ-PPh₂)(μ-H)₃(CO)₁₀(PPh₃) (8).     

Preparation and characterization of cobalt-containing P,N-ligands and an unusual palladium complex ion pair: their applications in amination reactions

Several cobalt-containing P,N-ligands, alkyne-bridged dicobalt phosphines [(μ-PPh₂CH₂PPh₂)Co₂(CO)₄(μ,η-Me₂NCH₂CCPR₂)] (4a: R=^tBu; 4b: R=Ph; 4c: R=Cy), were prepared from the reactions of corresponding alkynylphosphines Me₂NCH₂CCPR₂ (2a: R=^tBu; 2b: R=Ph; 2c: R=Cy) with a dppm-bridged dicobalt complex [Co₂(CO)₆(μ-P,P-PPh₂CH₂PPh₂)] 3. A unique palladium complex ion pair [(μ-PPh₂CH₂PPh₂)Co₂(CO)₄(μ,η-Me₂NCH₂CCP (^tBu)₂)Pd(η³-C₃H₅)]⁺[(η³-C₃H₅)PdCl₂]⁻7a was obtained from the reaction of 4a with [(η³-C₃H₅)PdCl]₂. Compounds 4a, 4b, and 4c are authentic cobalt-containing P,N-bidentate ligands and can be used for ligation of palladium from various sources such as Pd(OAc)₂ or [(η³-C₃H₅)PdCl]₂. Satisfactory efficiencies were observed for the amination reactions of aryl bromides with morpholine employing either a 4a-chelated palladium complex formed in situ or pre-formed 7a as the catalytic precursor.     

Reactions of a phosphido-bridged unsymmetrical diiron complex (η-C5Me5)Fe2(CO)4(μ-CO)(μ-PPh2) with various alkynes

A phosphido-bridged unsymmetrical diiron complex (η⁵-C₅Me₅)Fe₂(CO)₄(μ-CO)(μ-PPh₂) (1) was synthesized by a new convenient method; photo-dissociation of a CO ligand from (η⁵-C₅Me₅)Fe₂(CO)₆(μ-PPh₂) (2) that was prepared by the reaction of Li[Fe(CO)₄PPh₂] with (η⁵-C₅Me₅)Fe(CO)₂I. The reactivity of 1 toward various alkynes was studied. The reaction of 1 with ^tBuCCH gave a 1:1 mixture of two isomeric complexes (η⁵-C₅Me₅)Fe₂(CO)₃(μ-PPh₂)[μ-CHC(^tBu)C(O)] (3) containing a ketoalkenyl ligand. The reactions of 1 with other terminal alkynes RCCH (R=H, CO₂Me, Ph) afforded complexes incorporating one or two molecules of alkynes and a carbonyl group. The principal products were dinuclear complexes bridged by a new phosphinoketoalkenyl ligand, (η⁵-C₅Me₅)Fe₂(CO)₃(μ-CO)[μ-CR¹CR²C(O)PPh₂] (4a: R¹=H, R²=H; 4b: R¹=CO₂Me, R²=H; 4c: R¹=H, R²=Ph). In the cases of alkynes RCCH (R=H, CO₂Me), dinuclear complexes having a new ligand composed of two molecules of alkynes, a carbonyl group, and a phosphido group; i.e. (η⁵-C₅Me₅)Fe₂(CO)₃[μ-CRCHCHCRC(O)PPh₂] (5a: R=H; 5b: R=CO₂Me), were also obtained. In all cases, mononuclear complexes, (η⁵-C₅Me₅)Fe(CO)[CR¹CR²C(O)PPh₂] (6a: R¹=H, R²=H; 6b: R¹=H, R²=CO₂Me; 6c: R¹=H, R²=Ph) were isolated in low yields. The structures of 1, 4c, 5b, and 6a were confirmed by X-ray crystallography. The detailed structures of the products and plausible reaction mechanisms are discussed.     

Alkynylphosphanes as supports for mixed-metal Co4M (M = Ru, Os) fluoride complexes: Syntheses, structures and thermolysis studies

Treatment of the tetrameric group eight fluoride complexes [MF(μ-F)(CO)₃]₄ [M = Ru (1a), Os (1b)] with the alkynylphosphane, Ph₂PCCPh, results in fluoride-bridge cleavage and the formation of the air-sensitive monomeric octahedral complexes [MF₂(CO)₂(PPh₂CCPh)₂] [M = Ru (2a), Os (2b)] in high yield. The molecular structure of 2b reveals a cis, cis, trans configuration for each pair of ligands, respectively. The free alkyne moieties in 2 can be readily complexed to hexacarbonyldicobalt fragments by treatment with dicobalt octacarbonyl to afford [MF₂(CO)₂(μ-η¹:η²-PPh₂CCPh)₂{Co₂(CO)₆}₂] [M = Ru (3a), Os (3b)]. Evidence for an intramolecular non-bonded contact between a bound fluoride and a cobalt carbonyl carbon atom is seen in the molecular structure of 3a. Thermolysis of 3a at 50 °C results in fluoride dissociation to give [RuF(CO)₂(μ-η¹:η²-PPh₂CCPh)₂{Co₂(CO)₆}₂]⁺ (4), while no reaction occurred with the osmium analogue. Prolonged thermolysis at 120 °C in a sealed vessel of both 3a and 3b gave only insoluble decomposition products.     

W(η-PhCCPh)3(η-Ph2PCCPPh2) as a ligand to prepare homo- and hetero-nuclear cluster complexes

Reaction of W(η²-PhCCPh)₃(NMe₃) (1) and Ph₂PCCPPh₂ (dppa) produces W(η²-PhCCPh)₃(η¹-Ph₂PCCPPh₂) (2), which contains a pendant phosphine group. Treatment of 2 with W(CO)₄(NCMe)₂ yields [W(η²-PhCCPh)₃](μ,η²-Ph₂PCCPPh₂)[W(CO)₄(NCMe)] (3). Compound 2 reacts with Os₃(CO)₁₀(NCMe)₂ to afford Os₃(CO)₁₀[(μ,η²-Ph₂PCCPPh₂)W(η²-PhCCPh)₃]₂ (4), and reacts with Ru₃(CO)₉(NCMe)₃ to afford Ru₃(CO)₉[(μ,η²-Ph₂PCCPPh₂)W(η²-PhCCPh)₃]₃ (5). The crystal structures of 2 and 3 are determined by an X-ray diffraction study.     

Amination and Suzuki coupling reactions catalyzed by palladium complexes coordinated by cobalt-containing monodentate phosphine ligands with bis-trifluoromethyl substituents on bridged arylethynyl: Observation of some unusual metal-containing compounds

Two cobalt-containing bulky monodentate phosphines {[(μ-PPh₂CH₂PPh₂)Co₂(CO)₄][(μ,η-(^tBu)₂PCCAr]} (4cm: Ar = 3-CF₃C₆H₄; 4cmm: Ar = 3,5-(CF₃)₂C₆H₃) were prepared from the reaction of Co₂(CO)₆(μ-PPh₂CH₂PPh₂) (3) with each corresponding alkynes (^tBu)₂PCCAr. Both compounds were converted to their oxidized forms {[(μ-PPh₂CH₂PPh₂)Co₂(CO)₄][(μ,η-(^tBu)₂P(O)CCAr]} (4cmO: Ar = 3-CF₃C₆H₃; 4cmmO: Ar = 3,5-(CF₃)₂C₆H₃) in the presence of oxide. Further reactions of 4cm and 4cmm with Pd(OAc)₂ gave palladium complexes {[(μ-PPh₂CH₂PPh₂)Co₂(CO)₄][(μ,η-(^tBu)₂PCC(Ar)-κC¹)]Pd(μ-OAc)} 5cm (Ar = 3-CF₃C₆H₃) and 5cmm (Ar = 3,5-(CF₃)₂C₆H₂), respectively. By contrast, reactions of 4cm and 4cmm with Pd(COD)Cl₂ gave products, [{μ-P,P-PPh₂CH₂PPh₂}Co₂(CO)₃(μ-CO){μ,η-(^tBu)₂PCCAr}]-PdCl₂] 8cm and 8cmm, respectively, with unique bonding modes. Several crystallines of [(4cm)₂Pd₃(μ-Cl)(μ-CO)₂)(μ-Cl)]₂ (9) were obtained along with crystallines of 8cm during the crystallization process. The crystal structures of all three compounds, 4cmmO, 8cmm and 9 were determined by single-crystal X-ray diffraction methods. Fair to excellent efficiencies were observed for employing 4cmm/palladium salt as catalytic precursor in amination as well as in Suzuki coupling reactions.     

Preparation of cobalt-containing bulky monodentate phosphines with electron-withdrawing/donating substituents on bridged arylethynyl and their applications in Suzuki coupling reactions

Several cobalt-containing bulky monodentate phosphines (μ-PPh₂CH₂PPh₂)Co₂(CO)₄(μ,η-(^tBu)₂PCC(C₆H₄R)) (4a: R=H; 4b: R=p-F; 4cp: R=p-CF₃; 4cm: R=m-CF₃; 4d: R=p-OMe) were prepared from the reactions of (^tBu)₂PCC(R-C₆H₄) (2a: R=H; 2b: R=p-F; 2cp: R=p-CF₃; 2cm: R=m-CF₃; 2d: R=p-OMe) with Co₂(CO)₆(μ-PPh₂CH₂PPh₂) 3. Further reactions of 4a, 4b, 4cp, 4cm, and 4d with Pd(OAc)₂ yielded unique palladium complexes (μ-PPh₂CH₂PPh₂)Co₂(CO)₄(μ,η-(^tBu)₂PCC(C₆H₃R)-κC¹)Pd(μ-OAc) (5a: R=H; 5b: R=p-F; 5cp: R=p-CF₃; 5cm: R=m-CF₃; 5d: R=p-OMe, respectively). The strong electron-withdrawing substituents, -F and -CF₃, assist the ortho-metalation process during the formation of 5b, 5cp, and 5cm. The more positively charged palladium center in 5b (or 5cp, 5cm) enhances the probability for PhB(OH)₃⁻ to attack the metal center and the rate of reduction thereafter. DFT studies on the charges of these palladium centers support this assumption. The enhancement of the reaction rates of the Suzuki-Miyaura cross-coupling reactions using 5b, 5cp, and 5cm is thereby attributed to this effect.     

Regiospecific and sequential P-C bond activation/cluster transformations in the reaction of PhCCo2MoCp(CO)8 with the diphosphine ligands 2,3-bis(diphenylphosphino)maleic anhydride (bma) and 3,4-bis(diphenylphosphino)-5-methoxy-2(5H)-furanone (bmf)

Thermolysis of the mixed-metal cluster PhCCo₂MoCp(CO)₈ (1) with the diphosphine ligand 2,3-bis(diphenylphosphino)maleic anhydride (bma) in CH₂Cl₂ leads to the sequential formation of the phosphido-bridged cluster Co₂MoCp(CO)₅[μ₂,η²,η¹-C(Ph)CC(PPh₂)C(O)OC(O)](μ-PPh₂) (3) and the bis(phosphido)-bridged cluster Co₂MoCp(CO)₄[η³,η¹,η¹-C(Ph)CCC(O)OC(O)](μ-PPh₂)₂ (4). 3 and 4 have been isolated and characterized in solution by IR and NMR (¹H, ¹³C, and ³¹P) spectroscopies, and the solid-state structures have been established by X-ray diffraction analyses. Both clusters contain 48e- and exhibit triangular Co₂Mo cores. The structure of 3 reveals the presence of a phosphido moiety that bridges the Co-Co vector and a six-electron μ₂,η²,η¹-C(Ph)CC(PPh₂)C(O)OC(O) ligand that caps one of the Co₂Mo faces. The X-ray structure of 4 confirms that the five-electron η³,η¹,η¹- C(Ph)CCC(O)OC(O) ligand is σ-bound to the two cobalt centers in an η¹ fashion and π-coordinated to the molybdenum center through a traditional η³-allylic interaction. The reaction between PhCCo₂MoCp(CO)₈ and the chiral diphosphine ligand 3,4-bis(diphenylphosphino)-5-methoxy-2(5H)-furanone (bmf) proceeds similarly, furnishing the phosphido-bridged cluster Co₂MoCp(CO)₅ [μ₂,η²,η¹-C(Ph)CC(PPh₂)C(O)OCH(OMe)](μ-PPh₂) (6), followed by conversion to Co₂MoCp(CO)₄[η³,η¹,η¹-C(Ph)CCC(O)OCH(OMe)](μ-PPh₂)₂ (7). The identities of clusters 6 and 7 have been ascertained by solution spectroscopic methods and X-ray crystallography. The overall molecular structure of cluster 6 is similar to that of cluster 3, except that the P-C(furanone ring) bond cleavage occurs with high regioselectivity and high diastereoselectivity. The cleavage of the remaining P-C(furanone ring) bond in cluster 6 gives rise to the bis(phosphido)-bridged cluster 7, whose structure is discussed relative to its bma-derived analogue 4. The diastereoselectivity that accompanies the formation of 6 and 7 is discussed relative to steric effects within the Co₂Mo polyhedron. The cyclic voltammetric properties of cluster 3 have been examined, with three well-defined one-electron processes for the 0/+1, 0/−1, −1/−2 redox couples found. The composition of the HOMO and LUMO in 3 was established by extended Hückel MO calculations, with the data discussed relative to the parent tetrahedrane cluster 1.     

Carbon-carbon coupling on tetrahedral iridium clusters: X-ray molecular structures and multinuclear NMR studies of the two isomeric forms of [Ir4(CO)6(μ3-η-HCCPh)(μ2-η-C4H2Ph2)(μ-PPh2)2]

The reactions of [HIr₄(CO)₉(Ph₂PCCPh)(μ-PPh₂)] (1) or [Ir₄(CO)₈(μ₃-η²-HCCPh)(μ-PPh₂)₂] (2) with HCCPh gave two isomeric forms of [Ir₄(CO)₆(μ₃-η²-HCCPh)(μ₂-η⁴-C₄H₂Ph₂)(μ-PPh₂)₂] (3 and 4) in good yields as the only products. These compounds were characterized with analytical and spectroscopic data including ¹H, ¹³C and ³¹P NMR (1 and 2D) spectroscopy and their molecular structures were established by X-ray diffraction studies. Compounds 3 and 4 exhibit the same distorted butterfly metal polyhedral arrangement of metal atoms with two μ-PPh₂ that occupy different positions in the structures of the two isomers. Both molecules contain a HCCPh ligand bonded in a μ₃-η²-// mode to one of the wings of the butterfly and a metallacyclic ring, which resulted from head-to-tail coupling, in the case of [Ir₄(CO)₆(μ₃-η²-HCCPh){μ₂-η⁴-(H)CC(Ph)C(H)C(Ph)}(μ-PPh₂)₂] (3) and tail-to-tail coupling, in that of [Ir₄(CO)₆(μ₃-η²-HCCPh){μ₂-η⁴-(H)CC(Ph)C(Ph)C(H)}(μ-PPh₂)₂] (4), and which is linked to two metal atoms of the second wing of the butterfly.     

Reactions of 1,8-bis(diphenylphosphino)naphthalene with Os3(CO)12: C-H and C-P bond cleavage reactions

Reactions of Os₃(CO)₁₂ with 1,8-bis(diphenylphosphino)naphthalene (dppn) are described. Crystallographically characterised complexes isolated from a reaction carried out in refluxing toluene are Os₃(μ-H)₂{μ-PPh₂(nap)PPh(C₆H₄)}₂(CO)₆ (1), Os₃(μ-H){μ₃-PPh₂(nap)PPh(C₆H₄)}(CO)₈ (2) and Os₂(μ-PPh₂){μ-PPh₂(nap)}(CO)₅ (3) (nap=1,8-C₁₀H₆), while at r.t. in the presence of ONMe₃, only Os₃(CO)₁₁{PPh₂(1-C₁₀H₇)} (4) was isolated. While 1 and 2 contain ligands formed by metallation of a Ph group of dppn, as found also in complexes obtained from dppn and Ru₃(CO)₁₂, ligands in 3 and 4 are formed by cleavage of a P-nap bond, not found in the Ru series.     

A comparison between the reaction of P2Ph4 with [{Co2(CO)6}2(μ-η:μ-η-HOCH2CCCCCH2OH)] and the reaction of [Co2(μ-PPh2)2(CO)6] with HOCH2CCCCCH2OH

Reaction of P₂Ph₄ with the diyne-diol complex [{Co₂(CO)₆}₂(μ-η²:μ-η²-HOCH₂CCCCCH₂OH)] in toluene at 65 °C gives [{Co₂(μ-P₂Ph₄)(CO)₄}{Co₂(CO)₆}(μ-η²:μ-η²-HOCH₂CCCCCH₂OH)] (1). Thermolysis of 1 at 95 °C leads to [{Co₂(CO)₅}₂(μ-P₂Ph₄)(μ-η²:μ-η²-HOCH₂CCCCCH₂OH)](2) and (μ₂-PPh₂)(μ₂-CO)(CO)₇] (3). The structures of 1-3 have been established by X-ray crystallography. In 1, a pseudoequatorial P₂Ph₄ ligand bridges the cobalt-cobalt bond of a Co₂(CC)(CO)₄ unit. By contrast, in isomeric 2, a pseudoaxial P₂Ph₄ ligand spans two Co₂(CC)(CO)₅ units, a new coordination mode for [{Co₂(CO)₅L}₂(μ-η²:μ-η²-diyne)] complexes. Complex 3 arises from dehydration-cyclocarbonylation of the diyne-diol in 1 to give a 2(5H)-furanone, a process that has not been previously reported. Reaction of HOCH₂CCCCCH₂OH with [Co₂(μ-PPh₂)₂(CO)₆] at 80 °C in toluene gave [Co₃(μ-PPh₂)₃(CO)₆], [Co₂(CO)₆(μ-η²-HOCH₂CCCCCH₂OH)] and [Co₂{μ-η⁴-PPh₂C(CCCH₂OH)C(CH₂OH)CO}(μ-PPh₂)(CO)₄] (4). The regiochemistry of 4 was confirmed by X-ray crystallography.     

Reactions of rhenium and manganese carbonyl complexes with 1,8-bis(diphenylphosphino)naphthalene: Ligand chelation, C-H and C-P bond-cleavage reactions

Reaction of [Re₂(CO)₈(MeCN)₂] with 1,8-bis(diphenylphosphino)naphthalene (dppn) afforded three mono-rhenium complexes fac-[Re(CO)₃(κ¹:η¹-PPh₂C₁₀H₆)(PPh₂H)] (1), fac-[Re(CO)₃{κ¹:κ¹:η¹-(O)PPh₂C₁₀H₆(O)PPh(C₆H₄)}] (2) and fac-[ReCl(CO)₃(κ²-PPh₂C₁₀H₆PPh₂)] (3). Compounds 1-3 are formed by Re-Re bond cleavage and P-C and C-H bond activation of the dppn ligand. Each of these three complexes have three CO groups arranged in facial fashion. Compound 1 contains a chelating cyclometalated diphenylnaphthylphosphine ligand and a terminally coordinated PPh₂H ligand. Compound 2 consists of an orthometalated dppn-dioxide ligand coordinated in a κ¹:κ¹:η¹-fashion via both the oxygen atoms and ortho-carbon atom of one of the phenyl rings. Compound 3 consists of an unchanged chelating dppn ligand and a terminal Cl ligand. Treatment of [Mn₂(CO)₈(MeCN)₂] with a slight excess of dppn in refluxing toluene at 72 °C, gave the previously reported [Mn₂(CO)₈(μ-PPh₂)₂] (4), formed by cleavage of C-P bonds, and the new compound fac-[MnCl(CO)₃(κ²-PPh₂C₁₀H₆PPh₂)] (5), which has an unaltered chelating dppn and a terminal Cl ligand. In sharp contrast, reaction of [Mn₂(CO)₈(MeCN)₂] with slight excess of dppn at room temperature yielded the dimanganese [Mn₂(CO)₉{κ¹-PPh₂(C₁₀H₇)}] (6) in which the diphenylnaphthylphosphine ligand, formed by facile cleavage of one of the P-C bonds, is axially coordinated to one Mn atom. Compound 6 was also obtained from the reaction of [Mn₂(CO)₉(MeCN)] with dppn at room temperature. The XRD structures of complexes 1-3, 5, 6 are reported.     

From straight chain to macrocyclic complexes containing mixed sulfur/nitrogen donors and coordinated 1,3-diynes

The acid-mediated reaction of [{Co₂(CO)₆(μ-η²-HOCH₂CC-)}₂] (1) with the meta- and para-substituted aminothiophenols, 3-NH₂-C₆H₄SH and 4-NH₂-C₆H₄SH, affords the straight chain species, [{Co₂(CO)₆(μ-η²-(3-NH₂-C₆H₄S)CH₂CC-)}₂] (2) and [{Co₂(CO)₆(μ-η²-(4-NH₂-C₆H₄S)CH₂CC-)}₂] (3), respectively. The molecular structure of 3 reveals the presence of two isomeric forms differing in the relative disposition of the S-aryl groups. Conversely, reaction of 1 with the ortho-substituted aminothiophenol, 2-NH₂-C₆H₄SH, furnishes the 10-membered macrocyclic species [{Co₂(CO)₆}₂{cyclo-μ-η²:μ-η²-CH₂C₂C₂CH₂SC₆H₃-NH-2}] (4) along with the linear chain complex [{Co₂(CO)₆(μ-η²-(2-NH₂-C₆H₄S)CH₂CC-)}₂] (5). On the other hand, treatment of 1 with the ortho-substituted mercaptopyridine, 2-SH-C₅H₄N, in the presence of HBF₄ gives the salt [{Co₂(CO)₆(μ-η²-(2-S-C₅H₄NH)CH₂CC-)}₂](BF₄)₂ (6a) in good yield; work-up in the presence of base affords the neutral complex [{Co₂(CO)₆(μ-η²-(2-S-C₅H₄N)CH₂CC-)}₂] (6b). Single crystal X-ray diffraction studies have been reported on 3-5 and 6a.     

Reaction of [M(CO)4] (M = Ir, Rh) with cyclopropenyl tetrafluoroborate - Ring opening and coupling of cyclopropenyl ligands to form dinuclear metal complexes

Reaction of the iridium tetracarbonylate [PPN][Ir(CO)₄] (1a) with triphenylcyclopropenyl tetrafluoroborate [C₃Ph₃][BF₄] afforded two dinuclear species Ir₂(CO)₄(μ,η¹:η²-C₃Ph₃)(μ,η²:η³-C₃Ph₃) (2) and Ir₂(CO)₄(μ,η⁴:η⁴-C₆Ph₆) (3a) resulting from the ring opening and in the latter case, coupling of the resulting acyclic, propenyl ligands. The analogous reaction with [PPN][Rh(CO)₄] (1b) afforded only the rhodium analogue for 3a.     

Complexation and metallation of Ph2PCC(CH2)5CCPh2 in triosmium carbonyl clusters

Reaction of Ph₂PCC(CH₂)₅CCPh₂ with Os₃(CO)₁₀(NCMe)₂ affords Os₃(CO)₁₀(μ,η²-(Ph₂P)₂C₉H₁₀) (1) and the double cluster [Os₃(CO)₁₀]₂(μ,η²- (Ph₂P)₂C₉H₁₀)₂ (2), through coordination of the phosphine groups. Thermolysis of 1 in toluene generates Os₃(CO)₇(μ-PPh₂)(μ₃,η⁵-Ph₂PC₉H₁₀) (3) and Os₃(CO)₈(μ-PPh₂)(μ₃,η⁶-Ph₂P(C₉H₁₀)CO) (4). The molecular structures of 1, 3, and 4 have been determined by an X-ray diffraction study. Both 3 and 4 contain a bridging phosphido group and a carbocycle connected to an osmacyclopentadienyl ring, which are apparently derived from C-P bond activation and C-C bond rearrangement of the dpndy ligand governed by the triosmium clusters.     

Reactions of linked tetrahedron clusters [Co2(CO)6(μ-HC2CH2O)-]2R with Rh2(CO)4Cl2 to give mixed-metal linked alkyne-bridged butterfly clusters containing C2Co2Rh2 unit

The reactions of compound Rh₂(CO)₄Cl₂, 1 with [Co₂(CO)₆(μ-HC₂CH₂O)-]₂R (R = C₆H₄, 2; (COCH₂)₂, 3; C₆H₄-1,4-(CO)₂, 4; (COCH)₂, 5; (CO)₂, 6) in benzene at 60 °C produce five new mixed-metal linked clusters Rh₂Co₂(CO)₁₀(μ₄,η²-HC₂CH₂O-R-OCH₂C₂H-μ)Co₂(CO)₆ (R = C₆H₄, 7a; (COCH₂)₂, 7b; C₆H₄-1,4-(CO)₂, 7c; (COCH)₂, 7d; (CO)₂, 7e) and five known linked octahedral clusters [Rh₂Co₂(CO)₁₀(μ₄,η²-HC₂CH₂O-)]₂R (R = C₆H₄, 8a; (COCH₂)₂, 8b; C₆H₄-1,4-(CO)₂, 8c; (COCH)₂, 8d; (CO)₂, 8e), respectively. Treatment of clusters 7a-8e in benzene at room temperature under air for 24 h with stirring afford the precursor clusters 2-6, respectively. The structure of cluster 7a has been determined by single-crystal X-ray diffraction. The linked cluster 7apossesses two isomers A and B in its structures, the Rh₂(CO)₄ unit inserts into one of two Co-Co bonds and coordinates to the Co₂C₂ core forming one distorted closo-Rh₂Co₂C₂ octahedron framework which is connected to the Co₂C₂ tetrahedron unit via C₆H₄(OCH₂)₂-1,4 as a bridging ligand. All clusters were characterized by C, H elemental analysis, IR and ¹H NMR spectroscopy.     

Ligand substitution in HC(O)CCo3(CO)9 with 4,5-bis(diphenylphosphino)-4-cyclopenten-1,3-dione (bpcd): Diphosphine ligand fluxionality, decarbonylation of the formyl moiety and competitive P-Ph bond cleavage reactivity

The reaction of the formyl-capped cluster HC(O)CCo₃(CO)₉ (1) with the diphosphine ligand 4,5-bis(diphenylphosphino)-4-cyclopenten-1,3-dione (bpcd) in the presence of added Me₃NO leads to the production of the disubstituted cluster HC(O)CCo₃(CO)₇(bpcd) (2). Thermolysis of 2 in toluene at 60 °C gives the methylidyne-capped cluster HCCo₃(CO)₇(bpcd) (4) and the phosphido-bridged cluster Co₃(CO)₇[μ₂,η²,η¹-P(Ph)CC(PPh₂)C(O)CH₂C(O)] (5). Cluster 4 has been independently prepared from HCCo₃(CO)₉ and bpcd and shown to serve as the precursor to 5. The new clusters 2, 4, and 5 have been isolated and characterized in solution by IR and NMR (¹H and ³¹P) spectroscopies and their solid-state structures have been established by X-ray diffraction analyses. Both clusters 2 and 4 contain 48e- and exhibit triangular Co₃ cores with a chelating and bridging bpcd ligand in the solid state, respectively. The structure of 5 provides unequivocal support for the loss of the methylidyne capping ligand and P-Ph bond cleavage attendant in the activation of 4 and confirms the presence of the face capping seven-electron μ₂,η²,η¹-P(Ph)CC(PPh₂)C(O)CH₂C(O) ligand in the final product. The fluxionality displayed by the bpcd ligand in clusters 2 and 4 and the decarbonylation behavior of the formyl moiety in the former cluster are discussed relative to related alkylidyne-capped Co₃ derivatives.     

Cobalt-mediated oligomerization reactions of amino-substituted acetylene derivatives

Reactions of the aminoacetylenes Et₂N-CC-R (R = SiMe₃, SPh, PPh₂; 1a-c) with (η⁵-pentamethylcyclopentadienyl)bis(ethene)cobalt yield the corresponding (η⁵-pentamethylcyclopentadienyl)(η⁴-cyclobutadiene)cobalt complexes 2a-c. Treatment of 1-phenylthio-2-diethylaminoacetylene 1b with three equivalents of CpCo(CO)₂ leads to the 1,3-dicobalta-bicyclobutane derivative 3′b. The analogous compound 3′d and the trinuclear cobalt complex 4′d are obtained from the reaction of bis(diethylamino)acetylene (1d) with (η⁵-cyclopentadienyl)bis(ethene)cobalt. Treatment of 1d with excess Co₂(CO)₈ yielded unexpectedly a mixture of di- and tetranuclear cobalt-carbene complexes 7 and 8, most likely formed through interaction of oxygen. A designed route to 7 and 8 is found by reacting the tetraethyloxamide 6 with Co₂(CO)₈ and Co₄(CO)₁₂, respectively. The catalytic cyclotrimerization reaction of the aminothioacetylene derivative 1b with [CpCo(CO)₂] or [Co₂(CO)₈] leads to tris(phenylthio)-tris(diethylamino)benzene derivative 9. The new compounds have been characterized by NMR spectroscopy, mass spectrometry as well as by X-ray structure analyses for 3′d, 7 and 8. The molecular structure of 3′d in the crystal reveals the presence of a bicyclobutane framework with a Co-Co distance (2.36 Å) lying between a single and a double bond, whereas the former CC triple bond is completely ruptured (2.13 Å). The Co-C(carbene) distances in 7 and 8 are 1.93 and 1.95 Å, respectively.     

Synthesis, structures and comparative electrochemical study of 2,5-bis(trimethylsilylethynyl)thiophene coordinated cobalt carbonyl units

The reaction between 2,5-bis(trimethylsilylethynyl)thiophene and Co₂(CO)₈ or Co₂(CO)₆(X), (X = dppa, dppm), gave rise to the formation of substituted ethynylcobalt complexes containing one or two Co₂(CO)₆ or Co₂(CO)₄(X) units, 2-[Co₂(CO)₄(X){μ₂-η²-(SiMe₃)C₂}]-5-(Me₃SiCC)C₄H₂S (X = 2CO (1), dppa (3) or dppm (4)) and 2,5-[Co₂(CO)₄(X){μ₂-η²-SiMe₃C₂}]₂C₄H₂S (X = 2CO (2), dppa (5) or dppm (6)). Desilylation of the non-metallated and metallated alkynes in 3, 4 and 6 occurred on treatment with KOH and tetrabutylammonium fluoride to give 2-[Co₂(CO)₄(μ-X){μ₂-η²-SiMe₃C₂}]-5-(CCH)C₄H₂S (X = dppa (7), dppm (8)) and 2,5-[Co₂(CO)₄(μ-dppm){μ₂-η²-HC₂}]₂C₄H₂S (9), respectively. Crystals of 6 suitable for single-crystal X-ray diffraction were grown and the molecular structure of this compound is discussed. A comparative electrochemical study of all these complexes is presented by means of the cyclic and square-wave voltammetry techniques.