Trushar Adatia

Chemistry of phosphido-bridged dimolybdenum complexes. Part 3. Reinvestigation of the reaction between [Mo2(η-C5H5)2(CO)6] and P2Ph4; X-ray structures of [Mo2(η-C5H5)2(µ-PPh2)2(CO)2], [Mo2(η-C5H5)2(µ-PPh2)2(µ-CO)], and trans-[Mo2(η-C5H5)2(µ-PPh2)2O(CO)]

The thermal reaction of [Mo2(η-C5H5)2(CO)2] with P2Ph2 in toluene gives [Mo2(η-C5H5)2(µ-PPh2)2-(CO)2] in high yield. An X-ray diffraction study shows a Mo–Mo double bond [2.712(2)A] symmetrically bridged by two PPh2 groups, with a planar Mo2P2 core. Under u.v. irradiation, further decarbonylation occurs to give [Mo2(η-C5H5)2(µ-PPh2)2(µ-CO)], in which two PPh2 groups and a carbonyl ligand bridge a Mo–Mo triple bond of length 2.515(2)A. Oxidation of either of these complexes gives cis- and trans-[Mo2(η-C5H5)2(µ-PPh2)2(CO)]; the structure of the trans isomer has been determined by X-ray diffraction. Protonation of [Mo2(η-C5H5)2(µ-PPh2)2(CO)2] occurs across the metal–metal bond to give [Mo2(η-C5H5)2(µ-H)(µ-PPh2)2(CO)2][BF4].

Synthesis of ortho-modified mercapto- and piperazino-methyl-phenylboronic acid derivatives

Abstract The synthesis of 2-mercapto- and 2-piperazino- (methyl-phenyl)-4,4,5,5-tetramethyl-[1,3,2]dioxaborolanes 4 and 5 , respectively, is described and their inhibitory activity against serine proteases including thrombin was measured. Some of these compounds were studied in both the solid state and in solution, displaying no S–B coordination and only weak N–B coordination.

The heteronuclear cluster chemistry of the group IB metals—18. Synthesis, structural characterization and dynamic behaviour of the bimetallic hexanuclear group IB metal cluster compounds [M2Ru4H2(μ-dppf)(CO)12] [M = Cu, Ag or Au; dppf = Fe(η5-C5H5PPh2)2]. X-ray crystal structure of [Cu2Ru4(μ3-H)2(μ-dppf)(CO)12]

Abstract Treatment of a dichloromethane solution of the salt [N(PPh3]2]2[Ru4(μ-H)2(CO)12] with two equivalents of the complex [M(NCMe)4]PF6 (M = Cu or Ag) at −30°C, followed by the addition of one equivalent of 1,1′-bis(diphenylphosphino)ferrocene (dppf) affords the mixed-metal clusters [M2Ru49μ-H)2(μ-dppf)(CO)12] [M = Cu (1) or Ag (2)] in ca 45–60% yield. The analogous gold-containing species [Au12Ru4H2(μ-dppf)(CO)12] (3) was obtained in ca 70% yield by treating an acetone solution of [N(PPh3)2]2[Ru4(μ-H)2(CO)12] with a dichloromethane solution of the complex [Au2(μ-dppf)Cl2], in the presence of T1PF6. The novel cluster compounds 1–3 have been characterized by IR and NMR spectroscopy and the structure of 1 has been determined by a single-crystal X-ray diffraction study. The metal core structure of 1 consists of a tetrahedron of ruthenium atoms capped by a copper atom, with one of the CuRu2 faces of the CuRu3 tetrahedron so formed further capped by a second copper atom to give a capped trigonal bipyramidal skeletal geometry. The other two CuRu2 faces of the CuRu3 tetrahedron are each capped by a triply bridging hydrido ligand, the bidentate diphosphine ligand bridges the two coinage metals and each ruthenium atom is bonded to three terminal CO groups. The spectroscopic data of the silver- and gold-containing species 2 and 3 are closely similar to those of 1, which suggests that 2 and 3 adopt similar metal core structures to that established for 1. However, the possibility that the capped trigonal bipyramidal metal framework of 3 is distorted by the dppf ligand towards a capped square-based pyramidal skeletal geometry cannot be excluded with the evidence available. Variable-temperature 1H and 31P{1H} NMR studies show that, at ambient temperatures in solution, the metal frameworks of all of the clusters undergo dynamic behaviour involving coinage metal site exchange, even though the two Group IB metals are linked together by the bidentate diphosphine ligand dppf. Free energies of activation ( ΔG ‡ ) at the coalescence temperature of 47±1, 40±1 and ca 33 kJ mol−1 have been calculated for the skeletal rearrangements from the coalescence temperatures observed in the variable-temperature 31P{1H} NMR spectra of clusters 1, 2 and 3, respectively. These values of ΔG ‡ are compared with those of structurally related analogous clusters. In addition, the dppf ligand attached to the coinage metals in each of 1–3 is also stereochemically non-rigid in solution at room temperature and it undergoes a process involving inversion of configuration at the phosphorus atoms, together with twisting of the cyclopentadienyl rings. The skeletal rearrangement process and the fluxional behaviour of the dppf ligand are definitely independent for clusters 2 and 3.

Synthesis of Group 1B sandwich cluster compounds with [Pt3(µ-CO)3(PPh3)3] and the structural characterisation of [M{Pt3(µ-CO)3(PPh3)3}2]PF6(M = Au or Cu) by single-crystal X-ray techniques

Sandwich cluster compounds of the type [M{Pt3(µ-CO)3(PPh3)3}2]PF6[M = Cu (1a) or Au (1b)], where the Group 1 B metal is co-ordinated simulataneously to two planar [Pt3(µ-CO)3(PPh3)3]triangulo rings, have been synthesised from [Pt3(µ-CO)3(PPh3)4] and either [Cu(MeCN)4]PF6 or [Au(L)Cl](L = CO or Me2S) in the presence of an excess of TIPF6. Complexes (1a) and (1b) are both dark red crystalline solids and are isomorphous. They have been characterised using 31P-{1H} n.m.r. and single-crystal X-ray techniques.

Achiral, selective CCK2 receptor antagonists based on a 1,3,5-benzotriazepine-2,4-dione template.

Novel, achiral 1H-1,3,5-benzotriazepine-2,4(3H,5H)-diones have been prepared and structurally characterized. These compounds are potent CCK(2) receptor antagonists that display a high degree of selectivity over CCK(1) receptors.

Helical group 12 co-ordination. The X-ray crystal structure of a five-co-ordinate zinc(II) complex

Abstract The templated dimine-containing complexes, [M(SpyNpy 2 )](ClO 4 ) 2 ·0.5H 2 O {where M = Zn II , Cd II or Hg II }, exhibit chirality in solution (NMR) which is consistent with, and may be diagnostic of, a helical coordination array in these complexes as verified by the X-ray crystal structure of an enantiomer of the zinc(II) derivative.

Regiospecificity in reactions of alkynes and phosphines with the phosphido-bridged iron–cobalt complex [(OC)4Fe(μ-PPh2)Co(CO)3]

Abstract The iron–cobalt phosphido-bridged complex [(OC)4Fe(μ-PPh2)Co(CO)3] (1) can be prepared conveniently and in good yield from the reaction of [Co2(μ-PPh2)2(CO)6] with [Fe(CO)5]. A study of the reactivity of 1 towards symmetrical and unsymmetrical alkynes, R1CCR2 (R1=R2=CO2Me, Ph; R1=H, R2=Ph), has been undertaken. In all cases, five-membered ferracycle-containing products of the type [(OC)3Fe{μ-PPh2C(O)CR1CR2}Co(CO)3] (R1=R2=CO2Me (2a), Ph (2c); R1=H, R2=Ph (2b)), are initially obtained in which a molecule of CO and a molecule of R1CCR2 have been inserted regiospecifically into a CoP bond in 1. Decarbonylation of 2a occurs during its preparation or in low yield on its thermolysis to give the four-membered ferracyclic species [(OC)3Fe{μ-PPh2C(CO2Me)C(CO2Me)}Co(CO)3] (3a). Similar thermolysis of 2b results not only in the related decarbonylation product [(OC)3Fe(μ-PPh2CHCPh)Co(CO)3] (3b), but additionally in three other products all in low yield, namely the regioisomer of 3b, [(OC)3Fe(μ-PPh2CPhCH)Co(CO)3] (4b), the aldehyde-substituted complex [(OC)3Fe{μ-PPh2C(CHO)CPh}Co(CO)3] (5b) and the five-membered ferracycle-containing species [(OC)3Fe{μ-PPh2CHCPhC(O)}Co(CO)3] (6b). Treatment of 2a and 2b with PPhMe2 and P(OMe)3 results in substitution of an iron-bound carbonyl group to give, respectively, [(PhMe2P)(OC)2Fe{μ-PPh2C(O)C(CO2Me)C(CO2Me)}(μ-CO)Co(CO)2] (7a) and [{(MeO)3P}(OC)2Fe{μ-PPh2C(O)CHCPh}(μ-CO)Co(CO)2] (7b) in high yield. In contrast, substitution of a cobalt-bound carbonyl is achieved on reaction of 3a with PPhMe2 or PPh2H to give [(OC)3Fe{μ-PPh2C(CO2Me)C(CO2Me)}Co(CO)2(L)] (L=PPhMe2 (8a), PPh2H (9a)). Thermolysis of the secondary phosphine-substituted complex 9a results in phosphorushydrogen bond cleavage to give [(OC)3Fe{μ-PPh2C(CO2Me)CH(CO2Me)}(μ-PPh2)Co(CO)2] (10a). Single-crystal X-ray diffraction studies have been performed on complexes 7b, 8a and 10a.

Synthesis, structure, and dynamic behaviour of two isomeric triosmium clusters containing the ethoxyvinylidene (CCHOEt) and ethoxyethyne (CHCOEt) ligands respectively

The µ3-ethynyl compound [Os3H(CCH)(CO)9] reacts smoothly with ethanol as the solvent to give two isomeric ethanol adducts: [Os3H2(CCHOEt)(CO)9](1) and [Os3H2(CHCOEt)(CO)9](2), derived by ethoxy-group addition at the β- and α-carbon atoms respectively. Insertion of CHCOEt into Os–H bonds of [Os3H2(CO)10] gives the vinyl isomers [Os3H(CHCHOEt)(CO)10](3) and [Os3H(CH2COEt)(CO)10](4). Thermal decarbonylation of (3) leads to both (1) and (2) but a similar decarbonylation of (4) leads only to (2). Compound (2) was prepared alternatively by hydrogenation of [Os3(µ3-CHCOEt)(CO)10](5). X-Ray diffraction showed that the structure of (1) is closely related to that of the vinylidene compound [Os3H2(µ3-CCH2)(CO)9], while that of (2) contains the µ3-ethoxyethyne ligand CHCOEt roughly parallel to one OS–OS edge. Although this is related closely to the most common type of µ3-alkyne bridging, there are considerable distortions from this idealised geometry. Both (1) and (2) undergo rapid enantiomerisation leading to coalescence of hydride and diastereotopic methylene signals in their 1H n.m.r. spectra by a single process in each case. A minor isomer of (1) detected at low temperatures is more rapidly fluxional than the major one and rapidly interconverts with it at room temperature. Attempting to reverse the addition of ethanol which had given (1) and (2), these compounds were treated with CF3CO2H. Compound (1) gave [Os3H2(CCH)(CO)10]+ by loss of ethoxide ion, whereas (2) was protonated at the metal atoms to give [Os3H3(CHCOEt)(CO)9]+(6).

Acyl group flipping in heterodimetallic complexes; X-ray crystal structures of [(η5-C5H5)MoMn{µ-C(O)C6H11}(µ-PPh2)(CO)5] and [(η5-C5H5)MoMn{µ-C(O)-CH2CH2CH3}(µ-PPh2)(CO)6]

Photolytic reaction of the heterodimetallic complex [(η5-C5H5)MoMn(µ-H)(µ-PPh2)(CO)6] with alkenes gives µ-acyl complexes shown by an X-ray analysis of [(η5-C5H5)MoMn{µ-C(O)C6H11}(µ-PPh2)(CO)5] to contain the Mo–C–O–Mn grouping; reaction with CO results in reversible metal–metal bond cleavage and flipping of the µ-acyl co-ordination to Mo–O–C–Mn, as shown by an X-ray analysis on [(η5-C5H5)MoMn{µ-C(O)CH2CH2CH3}(µ-PPh2)(CO)6].

Synthesis of the cluster dianion [Os11C(CO)27]2– by pyrolysis and its reactions with electrophiles; X-ray structure analysis of the mixed-metal derivative [PMePh3][Os11C(CO)27{Cu(NCMe)}]·CH2Cl2 and the hydrido derivative [PMePh3][Os11C(CO)27H]

The new cluster species [Os11C(CO)27]2–(2) has been identified as one of the products resulting from the pyrolysis of [Os3(CO)12]. It reacts with [Cu(NCMe)4] BF4 to yield the monoanion [Os11C(CO)27{Cu(NCMe)}]–(4) and [Os11C(CO)27{Cu(NCMe)}2](5). The reaction of (2) with iodine-iodide produces a series of iodo-clusters [Os11C(CO)27I]–(8) and [Os11C(CO)27I2](9) which are converted back into (2) by addition of halide ions. The unstable monoanionic species [Os11C(CO)27{M(PMe2Ph)}]–[M = Au (3) or Cu (7)] are obtained on reaction of (2) with [M(PMe2Ph)]+, and further reaction of (3) yields [Os11C(CO)27{Au(PMe2Ph)}2](6). The dianionic cluster (2) reacts with acid to give the monoanion [Os11C(CO)27H]–(10) and [Os11C(CO)27H2](11). The reaction with Hg(C6Cl5)(O2CCF3) yields initially the unstable monoanion [Os11C(CO)27{Hg(C6Cl5)}]–(12) which is rapidly converted into the known cluster dianion [Os20Hg(C)2(CO)48]2–. X-Ray analysis of the [PMePh3]+ salts of (4) and (10) reveal identical Os11 core geometries, but in (4) the copper ligand occupies a µ3-bridging position, while the hydride in (10) appears to be located in an interstitial site.