Christopher J. Willis

Complexes of hybrid ligands. Synthesis of mixed-ligand, phosphino-alkoxide complexes of Pd2+: the crystal and molecular structure of the complex Ph2 PCH2C(CF3 )2OPdCl(PPh2Me)

Abstract The hybrid, bidentate, diarylphosphino-alkoxide ligand PPh 2 CH 2 C(CF 3 ) 2 O − , L 1 , gives the Pd 2+ bis- complex Pd(L 1 ) 2 , from which the chloride-bridged dinuclear complex [(L 1 )Pd(μ-Cl) 2 Pd(L 1 )] is made by reaction with PdCl 2 (PhCN) 2 . Cleavage of the dinuclear complex with monodentate ligands L 2 then gives Pd(L 1 )Cl(L 2 ) (L 2 =PPh 3 , PPh 2 Me, PPhMe 2 , PMe 3 , SMe 2 , or pyridine); NMR data show that PR 3 is cis to the phosphine site in L 1 in these complexes, but SMe 2 or pyridine are probably trans . A complete crystal and molecular structural determination has been made for cis -Pd(L 1 )Cl(PPh 2 Me). Crystals are monoclinic, space group P 2 1 / c , a = 10.821(1), b = 14.600(1), c = 18.674(2) A, β = 101.25(1)°, V = 2893 A 3 , Z = 4. Least-squares refinement on F of 361 variables using 3977 observations converged at a conventional agreement factor R = 0.025. The complex is square-planar, with the two phosphines cis ; the 5-membered chelate ring is in a dissymmetric envelope conformation. The PdP bonds differ in length, with that to the unidentate phosphine, 2.259(1) A, being significantly longer than that to the phosphine on the chelating ligand, 2.231(1) A.

Coordination modes of polydentate ligands. 4. The crystal and molecular structure of an oxo-bridged iron(III) complex containing a pentadentate imino-alkoxy ligand

Abstract In the presence of Fe3+, template condensation of the fluorinated keto-alcohol CH3C(O)CH2C- (CF3)2OH with the triamine CH3C(CH2NH2)3 leads to two products: a fully condensed, imino-alkoxy, iron(III) complex, Fe{CH3C[CH2NC(CH3)CH2C(CF3)2O]3}, and a partially condensed iron(III) complex, O{FeCH3C[CH2NC(CH3)CH2C(CF3)2O]2(CH2NH2)}2, in which two six-coordinate iron(III) centers are linked by an oxide ion. A complete crystal and molecular structure determination of the latter has been made. Crystals are monoclinic, space group C2/c, a= 13.886(4); b=23.206(5); c=15.241(4) A; β= 106.55(2)°; V=4708 A3; Z=4. Least-squares refinement on F of 322 variables using 2627 observations converged at a conventional agreement factor of 3.8%. The Fe to bridging oxide distance is 1.811(1) A, the FeFe distance 3.468 A, and the FeOFe angle 146.6(2)°. A comparison is made between this structure and those of natural hemerythrin systems.

“syn–anti- Isomerization” of the N-heptafluoroisopropylimine of hexafluoroacetone; steric effects or negative hyperconjugation?

The activation parameters for the syn–anti-isomerization of several N-alkyl and N-fluoroalkylimines of hexafluoroacetone have been obtained by dynamic 19F n.m.r. spectroscopy and have been interpreted in terms of steric effects, rather than negative hyperconjugation.

Preparation and structure of an anionic Cu2+ alkoxy complex containing a sixteen-membered, H-bonded, fluorinated macrocyclic ring

In the complex [Ph4P+]2[Cu{OC(CF3)2OH}4]2–, four-co-ordinate, square-planar Cu2+ lies at the centre of a 16-membered macrocycle held together by hydrogen-bonding between four fluorinated alkoxide ligands.

Condensation of hexafluoropane-2,2-diol into a hydrogen-bonded, 16-membered macrocyclic ligand complexing copper(II)

Abstract We have previously reported [1] on the ability of the stable gem-diol (CF3)2C(OH)2, (‘hexafluoroacetone hydrate’) to coordinate to a variety of transition metal ions. With neutral coligands, such as amines of phosphines, two types of complex are found, containing either the 4-membered ring (a) or the 6-membered ring (b). The latter appears to be formed by template condensation of two diol ligands on the metal ion. We have now found that, in the absence of coligand, four diol molecules may be coordinated to Cu2+ to give an anionic complex. Structural determination shows the metal to be at the centre of a 16-membered ring linked by four H-bond, as in (c). This structure is very similar to that found in the absence of metal, where two H-bonded protons occupy central positions [2].

Coordination modes of some fluorinated, potentially polydentate, ligands

Abstract Through the use of template condensation reactions, we have developed synthetic routes to a number of fluorinated ligands containing a number of donor atoms in combination with a fluorinated alkoxy group. Typical examples are: We find all of these to be capable of coordination to transition metals, generally giving stable, neutral, complexes. However, the mode of coordination of (i) and (ii) differs according to the donor atoms present in the chain, with a higher degree of coordination for X = N than for X = O. With ligand (iii), a ‘tripod’ mode of coordination is favoured, with the six donor sites surrounding a 3+ metal ion such as iron(III), cobalt(III), or a lanthanide(III) species.

NMR and synthetic studies on some fluorinated, sulfur-containing, complexes of Pd2+, Pt2+ and Rh3+

Abstract Starting with hexafluoroacetone and alkyl- or aryl-sulfides, we have synthesised new molecules of the type: The enhanced acidity of the -OH group enables these molecules to ionize and coordinate to metals through oxygen and sulfur as bidentate, uninegative, ligands [L − = RSCH 2 C(CF 3 ) 2 O − ], and we have isolated complexes of the types ML 2 and [(Ph 3 P) 2 ML] + (M = Pt 2+ , Pd 2+ ) and RhL 3 . On the basis of 19 F, 1 H and 31 P NMR spectra, several of the above complexes show isomerism in solution, which we attribute to the pyramidal geometry at coordinated sulfur. Variable-temperature NMR studies have been performed to investigate the dependence of the barrier to inversion on ligand structure and the identity of the metal.