Yvonne V. Roberts

Structural and electrochemical studies on trithia macrocyclic complexes of palladium

Abstract The single crystal X-ray structure of [Pd( 1 ) 2 ](PF 6 ) 2 ( 1 = 1,4,7-trithiacyclononane) shows a crystallographically centrosymmetric cation with a distorted octahedral stereochemistry about the Pd II centre with PdS eq 2.332(3) and 2.311(3) A for the equatorial thia donors, and PdS ax 2.952(4) A for the two apically coordinated donors. The crystals have space group C 2/ C , with a 17.879(8), b 15.627(13), c 11.476(8) A, β 125.92(4)° and Z = 4. Least squares refinement gave R = 0.0565 for 1153 unique observed reflections measured by counter diffracometry using Mo- K α radiation. This green complex undergoes a chemically reversible, one-electron oxidation in CH 3 CN, E pa = +0.65V, E pc = +0.56 V vs. Fc/Fc + , Δ E p = 84 mV. Oxidation of [Pd( 1 ) 2 ](PF 6 ) 2 by controlled potential electrolysis at +0.7 V affords an orange, ESR active product which may be tentatively assigned to the corresponding palladium(III) species. These results are contrasted with data for the related homoleptic thia complexes [Pd( L )] 2+ ( L = 1,4,8,11-tetrathiacyclotetradecane ( 2 ), 1,4,7,10,13,16-hexathiacyclooctadecane ( 3 )). The syntheses of the complexes cis -[Pd( 1 )Cl 2 ], cis -[Pt( 1 )Cl 2 ], cis -[Pd( 1 )(PPh 3 ) 2 ](PF 6 ) 2 and cis -[Pt( 1 )(PPh 3 ) 2 ](PF 6 ) 2 are also described.

Synthesis and structure of half-sandwich palladium(II) complexes of 1,4,7-trithiacyclononane ([9]aneS3) incorporating halide, phosphine and heterocyclic ligands

Reaction of PdCl2 with [9]aneS3(1,4,7-trithiacyclononane) in MeCN–CH2Cl2(3 : 1 v/v) afforded cis-[Pd([9]aneS3)Cl2] which can be converted into a range of half-sandwich palladium(II) complexes cis-[Pd([9]aneS3)Cl(L)]PF6[L = PPh3 or P(C6H11)3] and cis-[Pd([9]aneS3)L][PF6]2{L = 2PPh3, Ph2PCH2PPh2(dppm), Ph2PCH2CH2PPh2(dppe), (Ph2PCH2)3CMe, (Ph2PCH2)2[Ph2P(O)CH2]2 CMe, 2,2′-bipyridine (bipy) or 1,10-phenanthroline (phen)}. The single-crystal structures of cis-[Pd([9]aneS3)Cl(PPh3)]PF6 and cis-[Pd([9]aneS3)L][PF6]2{L = 2PPh3, dppm, (Ph2PCH2)2[Ph2P(O)CH2]CMe, bipy or phen} have been determined. They all show square-planar co-ordination of PdII by L and two S-donors of [9]aneS3, as well as an additional apical interaction with the third S-donor of [9]aneS3, Pd ⋯ Sap 2.990(2)A for cis-[Pd([9]aneS3)Cl(PPh3)]PF6, 2.948(13)A for cis-[Pd([9]aneS3)(phen)][PF6]2, 2.877(3)A for cis-[Pd([9]aneS3)(PPh3)2][PF6]2, 2.808(13)A for cis-[Pd([9]aneS3)(bipy)][PF6]2, 2.722(4) and 2.768(5)A for the two independent molecules of cis-[Pd([9]aneS3){(Ph2PCH2)2[Ph 2P(O)CH2]CMe}][PF6]2 and 2.698(3)A for cis-[Pd([9]aneS3)(dppm)][PF6]2. In the solid state there is, therefore, a general tendency for the third S-donor of [9]aneS3 to form a long-range apical interaction giving overall five-co-ordination at PdII. The length of this interaction is influenced strongly by the electronic properties of the ligand L and by the overall charge of the complex cation. The redox properties of these complexes are discussed.

Molecular clusters as models of metallic catalysts

Abstract A critical view of the use of molecular clusters as models of metallic catalysts and as means of modelling chemistry at the surface is presented. The major problems that still exist in the identification of surface adsorbed species and the bonding modes they adopt on reaction with the variety of different metal faces available on the surface of close-packed metal arrays are identified. Limitations have been placed on any direct comparisons because of the relatively small size of clusters under examination and the non-planar characteristics. The use of molecular clusters in this way has led to a much clearer understanding of the bonding mode adopted by a variety of chemisorbed species and can provide answers to long-standing problems.

A new mechanism for the rearrangement of the icosahedral carboranes

Abstract A new mechanism which involves the anticubeoctahedron as the complementary geometry is postulated to rationalise previously reported data on the rearrangement of various icosahedral carboranes.

Heteronuclear cluster formation: the synthesis and structure of the chloro-bridged tetranuclear complex [TlCl2Ru(PPh3)([9]aneS3)]2(PF6)2 incorporating a [RuCl2Tl2Cl2Ru] ladder ([9]aneS3= 1,4,7-trithiacyclononane)

Treatment of [RuCl2(PPh3)([9]aneS3)], formed in high yield by reaction of [RuCl2(PPh3)3] with [9]aneS3, with TIPF6 in CH2Cl2 at 273 K affords the yellow hetero-cluster species [TlCl2Ru(PPh3)([9]aneS3)]2(PF6)2 incorporating a [RuCl2Tl2Cl2Ru] ladder; dissolution of [TlCl2Ru(PPh3)([9]aneS3)]2(PF6)2 in acetone leads to precipitation of TlCl and the formation of the orange chloro-bridged dimer [RuCl(PPh3)([9]aneS3)]2(PF6)2.

The mechanism of carbonyl substitution reactions of Ir4(CO)12−nLn (n=0−3)

Abstract A mechanism in which the heterolytic fission of the metal-metal bond is considered to be the key initial step in the substitution reactions of the tetranuclear clusters Ir4(CO)12−nLn (n=0–3) is described.

Solid-state studies into the possible rearrangement mechanisms for the fluxional behaviour of the tetranuclear carbonyls M4(CO)12 and their derivatives

Abstract The deformation from an idealised geometry, observed in the solid state for a given cluster species, may indicate the paths taken by the cluster in ligand fluxionality processes. A number of single-crystal X-ray structures of M 4 (CO) 12− n (L) n clusters (M  Co, Rh, Ir; n = 1–5) have been examined in order to elucidate any geometric trends in their ligand envelope deformations. It has been revealed that the complementary geometries adopted by M 4 (CO) 12− n (L) n species may be both metal- and ligand-dependent. Iridium species adopt T d -cubeoctahedral structures, but the available data provide no clear picture for the complementary geometry adopted by cobalt or rhodium species. Additionally, tripodal ligands have been shown to stabilise D 3 h (icosahedral) ligand polyhedra.

Agostic Pd ⋯ H+⋯ NHR2 and apical Pd ⋯ NHR2 interactions: the synthesis and structures of [PdIICl2(H[9]aneN3)]+, the PdII–PdII dimer [(H[9]aneN3)Cl2Pd–PdCl2(H[9]aneN3)]2+, and [Pd(Me3[9]aneN3)(NCMe)2]2+

Long-range agostic Pd ⋯ H+⋯ NHR2 interactions are observed in the crystal structure of the protonated form of cis-[PdIICl2([9]aneN3)], while a direct apical Pd ⋯ NHR2 interaction is observed in the purple complex [Pd(Me3[9]aneN3)(NCMe)2](PF6)2.

The ligand polyhedral model and its application to the fluxional behaviour of M4(CO)12−n (M Co, Rh, Ir; n = 1, 2, 4 clusters☆

Abstract A number of mechanisms have been previously proposed to explain the observed fluxional behaviour of related cluster species of the general type M 4 (CO) 12− n L n (M  Co, Rh, Ir; n = 1, 2, 4). Here, a combination of metal core libration and an icosahedral-anticubeoctahedral-icosahedral ligand polyhedral rearrangement, arising from the ligand polyhedral model, is used to account for this observed behaviour. The ideas proposed are general and may be applied to all systems containing icosahedral, cubeoctahedral or anticubeoctahedral ligand shells.

On the mechanisms of fluxionality and isomerisation of [Fe3(CO)12–n{P(OMe)3}n](n= 1–3)

Possible alternative mechanisms based on the ligand polyhedral model have been examined to account for the dynamic behaviour and isomerisation of the triiron derivatives [Fe3(CO)12–n{P(OMe)3}n](n= 1–3). Carbonyl scrambling is considered to occur via two fundamental processes. First, a low-energy libration of the metal cluster unit within the ligand polyhedron and secondly, a higher-energy ligand polyhedral interconversion involving an anticubeoctahedral ligand array as the complementary geometry. Isomerisation is also believed to occur via related ligand polyhedral rearrangements.