Kenneth I. Hardcastle

Electron deficient bonding of benzoheterocycles to triosmium clusters: synthesis and applications to organic chemistry

Abstract A new synthetic methodology for the addition of carbon based nucleophiles to the carbocyclic ring of quinolines has been developed which is based on the electron deficient bonding of the C(8) carbon and the protective coordination of the nitrogen atom to the metal core in the complexes [Os3(CO)9(μ3-η2-C9H5(R)N)(μ-H)] (R can be a wide range of substituents in the 3-, 4-, 5- and 6-positions of the quinoline ring). These complexes react with a wide range of carbanions (R′Li, R′=Me, nBu, tBu, Bz, Ph, CHue605CH2, C2(CH2)3CH3, CH2CN, (CH3)2CCN, –CHS(CH2)2S–; CH2CO2tBu, R′MgBr, R′=CH3, CH2CHue605CH2) to give the nucleophilic addition products [Os3(CO)9(μ3-η3-C9H7(5-R′)N)(μ-H)] (2a–2l), after quenching with trifluoracetic acid, in isolated yields of 43–86%. Substitution at the 3- or 4-position is well tolerated giving the expected nucleophilic addition products [Os3(CO)9(μ3-η3-C9H6(3 or 4-R)(5-R′)N)(μ-H). The 6-substituted derivatives give >95% of the cis-diastereomer, [(Os3(CO)9(μ3-η3-C9H6(5-R′)(6-R)N)(μ-H)]. The stereochemistry is preserved even in the case of less bulky carbanions (R′=CH3). In the case of the 6-Cl derivative, a second product is obtained on reaction with the isobutyryl carbanion, [Os3(CO)9(μ3-η2-C9H5(6-Cl)(5-C(CH3)2CN)N)(μ-H)2] (4) which is the result of protonation at the metal core and rearrangement of the carbocyclic ring. The trans-diastereomer of the addition products obtained from the 6-substituted derivatives can be synthesized by reaction of the unsubstituted complex with R′Li followed by quenching with (CH3O)2SO2. Acetic anhydride can also be used as the quenching electrophile for the intermediate anions generated from R′Li [(trans-Os3(CO)9(μ3-η3-C9H6(6-CH3CO)(5-CH3)N)(μ-H)] (5). Nucleophilic addition occurs across the 3,4-bond in the cases where the 5-position is occupied by a substituent. The nucleophilic addition products can be rearomatized by reaction with DBU/DDQ or by reaction of the intermediate anion with trityl cation or DDQ. The resulting rearomatized complexes can be cleanly cleaved from the cluster by reflux in acetonitrile under a CO atmosphere yielding the functionalized quinoline and Os3(CO)12 as the only two products. An overview of this previously reported work along with additional examples of this novel chemistry is given here as well as an extention of the synthesis of the electron deficient triosmium clusters to a wide range of heterocycles structurally related to quinoline. These complexes include those containing the heterocycles: phenanthridine (7), 5,6-benzoquinoline (8), 2-CH3-benzimidazole (9), 2-methyl benzotriazole (10), 2-methyl-benzoxazole (11), 2-R-benzothiazole (R=H, 12; CH3, 13) and quinoxaline (14). The solid state structures of 7–10, 12, and 14 are reported.

Overcoming a Longstanding Challenge: X-Ray Structure of a [Co2(CO)6]-Complexed Propargyl Cation

After two decades of thwarted efforts, the first X-ray structure analysis of a [Co2(CO)6]-complexed propagyl cation, the BF4 salt of 1, has been reported. The carbocationic center is almost ideally sp2-hydbridized, while the metal clusters exhibit substantial structural inequivalency.

Some pyridine-2-thiolato and 6-methylpyridine-2-thiolato complexes of manganese: crystal structure of [Mn2(μ-pyS)2(CO)6] (pyS = pyridine-2-thiolato ligand)

Abstract The complexes [Mn 2 (μ-pyS) 2 (CO) 6 ] ( 1 ) and [Mn 2 (μ-MepyS) 2 (CO) 6 ] ( 2 ), where pySH = pyridine-2-thiol and MepySH = 6-methylpyridine-2-thiol, have been made by reaction of Mn 2 (CO) 10 with the appropriate pyridinethiol in refluxing hexane. In these complexes pyS and MepyS act as both six electron donor chelating and bridging groups which form four-membered N,S chelate rings at one metal centre and bridge to the other metal atom through sulphur. Complex 2 reacts with PPh 3 and Ph 2 PCH 2 PPh 2 (dppm) in refluxing cyclohexane to give [Mn(MepyS)(PPh 3 (CO) 3 ] ( 3 ) and [Mn(MepyS)( η 1 -dppm) 2 (CO) 2 ] ( 4 ) respectively. The crystal structure of 1 was determined.

Synthesis and structures of two isomers of [Re3Ru(S)(C5H4N)(C5H4NS)2(CO)11] which differ in the distribution of pyridine-2-thionato ligands between doubly- and triply-bridging positions

Abstract The pyridine-2-thionato (pyS) bridged compound [Re2(pyS)2(CO)6] reacts with [Ru3(CO)12] to give various tetranuclear compounds built from Re(pyS)(CO)3 and Ru(CO)x (x = 2, 3 or 4) units: [ReRu3(S)(C5H4N)(CO)14], [Re2Ru2(S)(C5H4N)(pyS)(CO)13], and [Re3Ru(S)(C5H4N)(pyS)2(CO)11] as two isomers. X-ray structures of these isomers show that one contains two doubly-bridging pyS ligands and the other one doubly- and one triply-bridging pyS ligands.

Cobalt-templated radical processes: inter- and intramolecular coupling of propargyl radicals

Abstract A novel method for radical Cue5f8C bond formation in the α-position to Co 2 (CO) 6 -clusters has been elaborated. The two-dimensional exploration of the process resulted in the discovery of structurally diverse O- and S-containing organic molecules capable of acting as efficient mediators in reductive coupling reactions, and in the elaboration of the preparative synthesis of 3,4-disubstituted 1,5-alkadiynes and carbocycles with eight- and nine-membered rings.

Methylene chain length and coordination geometry in triosmium clusters containing diphosphine ligands X-ray crystal structures of [Os3(CO)10{μ-Ph2P(CH2)n}](n = 4 or 5) and [Os3(CO) 8{μ-Ph2PCH2PPh2}2]

Abstract The bis-acetonitrile compound [Os3(CO)10(MeCN)2] and the butadiene compound [Os3(CO)10(η4-cis-C4H6)] react with dppp {dppp = Ph2P(CH2)5PPh2} to give only [Os3(CO)10(μ-dppp)] (1). Protonation of 1 with trifluoroacetic acid le [(μ-H)Os3(CO)10(μ-dppp)]+ (2) with the hydride bridging the same osmium atoms as the dppp. The bridging dppp compound [Os3(CO)10(μ-dppp)] (1) reacts with dppp at 110°C to give [Os3(CO)9(η1-dppp)(μ-dppp)] (4) whereas [Os3(CO)10(μ-dppm)] under the same conditions reacts with dppm (dppm = Ph2PCH2PPh2) to give [Os3(CO)8(μ-dppm)2] (5). Protonation of 5 with trifluoroacetic acid gives [(μ-H)Os3(CO)8(μ-dppm)2]+ (6) with the hydride bridging the unsubstituted Os — Os edge. The monoacetonitrile compound [Os3(CO)11(MeCN)] reacts with dppp at 0°C to give two compounds: [Os3(CO)11(η1-dppp)] (7) containing one coordinated and one free phosphorus atoms and [{Os3(CO)11}2(μ-dppp)] (8) with one dppp ligand bridging two Os3(CO)11 moities. Solid-state structures for 1, 5 and the previously reported cluster [Os3(CO)10(μ-dppb)] (3) {dppb = Ph2P(CH2)PPh2) are reported. Compound 1 crystallizes in the space group P212121 with unit cell parameters a = 11.770(2) A , b = 16.957(3) A , c = 21.681(5) A , V = 4327(2) A 3 and Z = 4 . Least-squares refinement of 6188 reflections gave a final agreement factor of R = 0.077 (Rw = 0.087). Compound 3 crystallizes in the space group P21/c with unit cell parameters a = 12.361(2) A , b = 16.804(2) A , c = 20.935(2) A , β = 116.66(11)°, V = 3886(2) A 3 and Z = 4 . Least-squares refinement of 2284 reflections gave a final agreement factor of R = 0.028 (Rw = 0.032). Compound 5 crystallizes in the space group Pca21 with unit cell parameters a = 21.398(3) A , b = 15.684(4) A , c = 18.219(4) A , V = 6115(4) A 3 and Z = 4 . Least-squares refinement of 5376 reflections gave a final agreement factor of R = 0.060 (Rw = 0.062).

Triosmium clusters containing bridging sulphur, hydrido, and diphosphine ligands: A study of hydride site preferences and mobility

Abstract Reaction of dppm (Ph 2 PCH 2 PPh 2 ) with [OS 3 (μ-H) 2 (μ 3 -S)(CO) 9 ] in refluxing toluene leads to the cluster [Os 3 (μ-H) 2 (μ 3 -S)(CO) 7 (dppm)] ( 1 ) (34% yield), the crystal structure of which has been determined. If the reaction is carried out at higher temperatures in refluxing octane, it gives the known cluster [Os 3 (CO) 8 (μ-dppm) 2 ] (11%) in addition to 1 . Cluster 1 is protonated to give [Os 3 (μ-H) 3 (μ 3 - S)(CO) 7 (dppm)] + , isolated as its hexafluorophosphate salt. The bridging dppm compound [Os 3 (CO) 10 (dppm)] reacts with RSH (R ue5fb Ph, or 4-MeC 6 H 4 ) in refluxing toluene to give the thiolato hydrido clusters [Os 3 (μ-H)(μ-SR)(CO) 8 (dppm)], which on protonation with trifluoroacetic acid give the protonated species [Os 3 (μ-H) 2 (μ-SR)(CO) 8 (dppm)] + , isolated as their hexafluorophosphate salts. We have examined the hydride coordination sites with respect to the position of the μ-dppm ligand and the effect of the μ-dppm ligand on the mobility of hydrides in these complexes.

Conversion of the cluster [Os3(CHCFc)(CO)10] (CHCFc = ethynylferrocene) into [Os3(S)(CHCFc)(CO)9] by reaction with sulphur. Crystal structures of these clusters and of [Os3H(C2Fc)(CO)9]

Abstract By application of a method established for various alkynes, the cluster [Os3(CO)10(MeCN)2] was treated with ethynylferrocene (CHCFc) to give the alkyne cluster [Os3(μ3-CHCFc)(μ-CO)(CO)9] (1). This cluster loses CO thermally and by visible irradiation to form the hydrido-ferrocenylethynyl cluster [Os3H(μ3-C2Fc) (CO)9] (2), but if the decarbonylation is carried out in the presence of sulphur at room temperature under visible irradiation, the cluster [Os3(μ3-S)(μ3-CHCFc)(CO)9] (3) is formed instead. The crystal structures of 1, 2, and 3 are reported. Clusters 1 and 3 are both 48-electron clusters containing μ3-CHue5fcCFc ligands but, whereas 1 contains three Osue5f8Os bonds, 3 contains only two. In 3 the triply bridging ligands occupy opposite faces of the Os3 triangle, with the osmium atoms at the open edge of the triangle having σ-bonds to the alkyne ligand. The structure of 1 and the known structure of [Os3(PhC2Ph)(CO)10] are closely related, although cluster 1 contains one bridging CO ligand and the latter two semi-bridging CO ligands. The fluxionality of cluster 1 is considered in the light of these different structures.

Triosmium clusters derived from the reactions of thioureas with dodecacarbonyltriosmium: Crystal structures of [Os3(CO)11{η1-SC(NMe2)2}], [Os3(CO)9(μ-OH)(μ-OMeOCO){η1-SC(NMe2)2}] and [(μ-H)Os3(CO)9{μ3-NHC(S)NH2}]

AbstractThe reaction of [Os3(CO)12] with tetramethylthiourea in the presence of a methanolic solution of Me3NO·2H2O at 60° yields the compounds [Os3(CO)11{η1-SC(NMe2)2}] (1) in 56% yield and [Os3(CO)9(μ-OH)(μ-MeOCO){η1-SC(NMe2)2}] (2) in 10% yield in which the tetramethylthiourea ligand is coordinatedvia the sulfur atom at an equatorial position. Compound2 is a 50 e− cluster with two metal-metal bonds and the hydroxy and methoxycarbonyl ligands bridging the open metal-metal edge. In contrast, the analogous reaction of [Os3(CO)12] with thiourea gives the compounts [(μ-H)Os3(CO)10{μ-NHC(S)NH2}] (3) in 8% yield and [(μ-H)Os3(CO)9{3-NHC(S)NH2}] (4) in 30% yield. In3, the thioureato ligand bridges two osmium atomsvia the sulfur atom, whereas in4 in addition to the sulfur bridge, one of the nitrogen atoms of thioureato moiety bonds to the remaining osmium atom. The decacarbonyl compounds 3 can also be obtained in 50% yield from the reaction of [Os3(CO)10(MeCN)2] with thiourea at ambient temperature. Compound3 converts to4 (65%) photochemically. Compound1 reacts with PPh3 and acetonitrile at ambient temperature to give the simple substitution products [Os3(CO)11(PPh3)] and [Os3(CO)11(MeCN)], respectively, while with pyridine, the oxidative addition product [(μ-H)Os3(CO)10(μ-NC5H4] is formed at 80°C. All the new compounds are characterized by IR,1-H-NMR and elemental analysis together with the X-ray crystal structures of1,2 and4. Compound1 crystallizes in the triclinic space group Pn