Alan J. Holder

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.

Stabilisation of trivalent platinum by structurally accommodating thiamacrocycles

The complex cation [Pt(1)2]2+[(1)= 1,4,7-trithiacyclononane] shows a quasi square based pyramidal structure with one non-bonding sulphur donor atom; electrochemical oxidation at +0.5 V. vs. Fc0/Fc+(Fc = ferrocene) at 20 °C in MeCN affords a paramagnetic platinum(III) species.

Stabilisation of mononuclear palladium(III). The single crystal X-ray structure of the [Pd(L)2]3+ cation (L = 1,4,7-trithiacyclononane)

Oxidation of the green [Pd(1)2]2+ cation [(1)= 1,4,7-trithiacyclononane] in 70% aqueous HClO4 affords the red [Pd(1)2]3+ cation, the single crystal X-ray structure of which shows a tetragonally distorted geometry about the PdIII centre with Pd–S(1) 2.5448(15), Pd–S(4) 2.3558(14), and Pd–S(7) 2.3692(15)A.

Silver thioether chemistry: Synthesis, X-ray crystal structure and redox properties of [Ag([18]aneS6)]+ ([18]aneS6 = 1,4,7,10,13,16-hexathiacyclooctadecane)

Abstract Reaction of AgNO3 with 1 molar equivalent of [18]aneS6 ([18]aneS6 = 1,4,7,10,13,16-hexathiacyclooctadecane) in water-MeOH (1:1 v/v) affords the complex cation [Ag([18]aneS6)]+. [Ag([18]aneS6)]PF6 crystallizes in the monoclinic space group I2/m with a = 5.295(4), b = 13.959(10), c = 13.951(9) A, β = 95.15(10)°, V = 1027 A3, Dc = 1.983 g cm−3, Z = 2. The complex cation has C2h(2/m) symmetry with AgI bound to all six thia donors of [18]aneS6 with two short [AgS(1) = 2.6665(12) A] and four significantly longer (AgS(4) = 2.7813(10) A) AgS distances. This 2+4 coordination of [18]aneS6 reflects the tendency of the d10 Ag+ ion to increase its coordination number with soft donor ligands. Chemical oxidation of [Ag([18]aneS6)]+ and [Ag([9]aneS3)2]+ at 293 K in highly acidic media affords the corresponding stable AgII species, which have been identified by ESR and UV—vis spectroscopy. These AgII species can only be generated electrochemically in MeCN at 293 K as transient intermediates. The enhanced stabilization of [M([9]aneS3)2]2+ (M = AgII) and [M([9]aneS3)2]3+ (M = FeIII, NiIII, PdIII) under acidic conditions is discussed.

Gold thioether chemistry: synthesis, structure, and redox interconversion of [Au([9]aneS3)2]+/2+/3+([9]aneS3= 1,4,7-trithiacyclononane)

The crystal structure of [Au([9]aneS3)2]PF6 shows distorted tetrahedral S4 co-ordination at AuI with one [9]aneS3 bound in a unidentate manner [Au(1)–S(11) 2.302(6)A], and the other bound asymmetrically through three S-donors [Au(1)–S(21) 2.350(7), Au(1)–S(24) 2.733(8), Au(1)–S(27) 2.825(8)A]; oxidation of this complex affords the AuIII analogue [Au([9]aneS3)2]3+ which has a distorted octahedral stereochemistry [Au(1)⋯ S(1) 2.926(4), Au(1)–S(4) 2.348(4), Au(1)–S(7) 2.354(4)A]; the intermediate paramagnetic AuIII species has been identified by e.s.r. spectroscopy.

Palladium(II)/(III) complexes of triaza macrocycles: synthesis and single crystal X-ray structures of [PdIII(tacn)2]3+ and [PdII(tacn)(tacnH)]3+(tacn = 1,4,7-triazacyclononane)

The complex cation [Pd(tacn)2]2+(tacn = 1,4,7-triazacyclononane) shows a one-electron oxidation at E½=+0.07 V vs. Fc/Fc+(ferrocene/ferrocinium) to afford the stable mononuclear PdIII species [Pd(tacn)2]3+, which has a tetragonally-distorted octahedral structure with Pd–N(1)= 2.180(9), Pd–N(4)= 2.118(9), Pd–N(7)= 2.111(9)A.

Homoleptic hexathia complexes of rhodium. The synthesis, electrochemistry, and single-crystal X-ray structure of [RhL2][PF6]3(L = 1,4,7-trithiacyclononane)

Reaction of [Rh(H2O)6]3+ with 2 molar equivalents of 1,4,7-trithiacyclononane (L) gives the complex cation [RhL2]3+. The single-crystal X-ray structure of [RhL2][PF6]3 shows a centrosymmetric complex around octahedral RhIII with Rh–S 2.332(2)A. The crystals are monoclinic, space group I2/m(alternative setting of C2/m, no. 12), with a= 11.329(3), b= 9.692(3), c= 14.909(4)A, β= 101.77(2)°, and Z= 2. Cyclic voltammetry of [RhL2][PF6]3 in MeCN (0.1 mol dm–3 NBun4PF6) at 20°C at platinum electrodes shows two chemically reversible reductions at 1E½=–0.71 V, ΔEp= 71 mV and 2E½=–1.08 V, ΔEp= 127 mV vs. ferrocene–ferrocenium, which are assigned to RhIII–RhII and RhII–RhI redox couples respectively.

Mercury thioether chemistry: The synthesis and structure of [Hg([9]aneS3)2](PF6)2 ([9]aneS3 = 1,4,7-trithiacyclononane)

Abstract Reaction of HgSO4 with 2 molar equivalents of [9]aneS3 in refluxing H2O-MeOH (1:1 v/v) for 1 h affords a colourless solution from which the complex [Hg([9]aneS3)2](PF6)2 can be isolated by addition of NH4PF6. [Hg([9]aneS3)2](PF6)2· 1 3 H2O crystallizes in the monoclinic space group I2/a, with a = 11.8667(10), b = 15.1631(23), c = 14.454(4) A, β = 90.224(19)°, V = 2600.7 A3, Dc = 2.18 g cm−3, Z = 4. The single crystal X-ray structure of the complex shows a crystallographically centrosymmetric cation with hexathia coordination at mercury(II), with HgS(1) = 2.728(3), HgS(4) = 2.638(3) and HgS(7) = 2.712(3) A. This structure closely resembles that of the silver(I) analogue, [Ag([9]aneS3)2]+, which also shows hexathia coordination. Cyclic voltammetry of [Hg([9]aneS3)2]2+ shows a chemically reversible reduction at E1/2 = −0.15 V (ΔEP = 80 mV) vs Fc/Fc+ at a scan rate of 90 mV s−1.

Copper thioether chemistry: The synthesis and single crystal X-ray structures of [Cu2([18]aneS6)(NCMe)2](ClO4)2 and [Cu([9]aneS3)(AsPPh3)](ClO4)

Abstract Reaction of [18]aneS 6 with two molar equivalents of [Cu(NCMe) 4 ](ClO 4 ) in CH 2 Cl 2 -MeCN affords the binuclear copper(I) complex [Cu 2 ([18]aneS 6 )(NCMe) 2 ](ClO 4 ) 2 . The single crystal X-ray structure of the complex shows a centrosymmetric cation with two tetrahedral copper(I) centres each coordinated to three thioether S-donors of [18]aneS 6 ,CuS(1) = 2.3200(15), CuS(4) = 2.3415(16), CuS(7) = 2.3250(15) A, and to one MeCN molecule, CuN(1) = 1.939(5) A, to give an overall NS 3 -donation at the metal centres. Additionally, S(7′) shows a long-range interaction, Cu …S(7′) = 3.318(2) A thus distorting the coordination geometry of the metal ion towards trigonal bipyramidal. The metal-metal separation of 4.428(2) A suggests that there is no significant interaction between the copper centres of the dimer. Reaction of [9]aneS 3 with one molar equivalent of [Cu(NCMe) 4 ](ClO 4 ) in refluxing MeCN in the presence of ligands, L, affords the adducts [Cu([9]aneS 3 )L] + (L = PPh 3 , AsPh 3 ). The single crystal X-ray structure of the complex [Cu([9]aneS 3 )(AsPh 3 )](ClO 4 ) shows tetrahedral AsS 3 coordination at copper(I) with [9]aneS 3 bound facially to the metal centre, CuS = 2.303(6), CuAs = 2.322(4) A.

π-Effects in thioether macrocyclic complexes: the stabilisation and structure of the low-spin FeIII thioether complex [Fe([9]aneS3)2]3+

Oxidation of [Fe([9]aneS3)2]2+ to [Fe([9]aneS3)2]3+ leads to an elongation of the Fe–S bonds from 2.251 (1), 2.241(1), 2.259(1)A in the 2+ cation to 2.280(3), 2.2846(25), 2.276(25)A in the 3+ cation giving, for the first time, direct structural evidence for the π-acceptor properties of thioether crowns.