Andrew W.G. Platt

Structures and catalytic properties of triphenylphosphine oxide complexes of scandium and lanthanide triflates

Abstract The complexes M(OTf) 3 (Ph 3 PO) 4 where M=lanthanide metals and scandium have been prepared and characterised in the solid state by single crystal X-ray diffraction, infrared spectroscopy and elemental analysis. All the complexes have the ionic structure [M(OTf) 2 (Ph 3 PO) 4 ] + [OTf] − . Single crystal X-ray structures for M=Sc, Nd and Lu are reported. In the complexes of the early lanthanides (LaNd) the metals are seven-coordinate with one monodentate, one bidentate triflate. The smaller lanthanide ions, and scandium, have six-coordinate structures with an approximate octahedral coordination about the metal where both triflates are bound as monodentate ligands. The solution structures have been analysed by electrospray mass spectrometry, which indicates that extensive ligand redistribution occurs. The complexes catalyse the Friedel Crafts acylation, alkenylation and alkylation of activated aromatics with modest increases in selectivity compared to the same reactions using scandium triflate.

Synthesis of tripodal tris-phosphonate ligands and the structure of the dimeric complex [Ce(NO3)3{(EtO)2P(O)CH2)3C6Me3]2

Abstract The tris-phosphonates 1,3,5 [(RO)2P(O)CH2]32,4,6 Me3C6 (=L–R) have been prepared from the corresponding tribromide and phosphites (RO)3P for R=Me, Et, iPr and Bu). The phosphonates react with lanthanide nitrates to give dimeric complexes Ln(NO3)3L2Ln(NO3)3. The X-ray crystal structure of the cerium(III) complex is reported. The behaviour of the complexes in solution has been examined by electrospray mass spectrometry and shows that the complex undergoes extensive ligand redistribution reactions in solution with no evidence for the presence of dimeric species. Molecular modelling calculations show that the tris-chelate monomer is unstable principally due to strain of the aromatic ring.

Structures and catalytic properties of complexes of bis(diphenylphino)methane dioxide with scandium and lanthanide trifluoromethane sulfonates

Abstract Complexes of scandium and lanthanide triflates with bis(diphenylphosphino)methane dioxide (Ph2P(O)CH2P(O)Ph2L) have been prepared and have the general formulae Sc(OTf)3L3, La(OTf)3L41.5H2O and Ln(OTf)3L3H2O3.5H2O. The structures show that the phosphine oxides act as bidentate chelates, and whilst triflate ions are not coordinated to the metals some hydrogen bond with the methylene protons in the ligand. The solution properties have been investigated using electrospray mass spectrometry and 31P NMR spectroscopy. The catalytic acylation of anisole has been investigated for the ytterbium and scandium complexes with the latter showing no activity.

Lanthanide nitrate complexes of tri-isobutylphosphine oxide: solid state and CD2Cl2 solution structures.

The complexes Ln(NO(3))(3)L(3) between Ln(NO(3))(3) and (i)Bu(3)PO (=L) have been prepared for Ln = La-Lu (excluding Pm). The isolated complexes have been characterized by infrared spectroscopy, mass spectrometry, and elemental analysis. The single crystal X-ray structures have been determined for representative complexes across the series Ln = Ce, Pr, Nd, Sm, Gd, Dy, Ho, Er, Tm, and Yb and show the coordination geometry around the metal to be the same with 9-coordinate lanthanide ions and bidentate nitrates. Subtle changes in the coordination of the nitrate ligand occur from Sm onward. Changes in the infrared spectra correlate well with changes in the X-ray structures. Solution properties have been examined by variable temperature multinuclear ((1)H, (13)C, (15)N, and (31)P) NMR spectroscopy in CD(2)Cl(2). The spectra of complexes of the early lanthanides are consistent with the presence of a single species in solution while those of the heavier lanthanides show that more than one complex is present in solution and that two inequivalent phosphorus environments are observable at low temperature. The fluxional behavior is lanthanide dependent with smaller ions giving static structures at higher temperature. Complexes with tricyclohexylphosphine oxide show that the dynamic NMR behavior is also related to the size of the ligand. Analysis of the lanthanide induced shifts indicates minor changes in solution structure occur from Sm onward which correlate well with the solid state structures.

Complexes of lanthanide nitrates with tri tert butylphosphine oxide

Reaction of lanthanide nitrates with (t)Bu(3)PO (=L) lead to the isolation of complexes Ln(NO(3))(3)L(2)·H(2)O·nEtOH (Ln = La (1), Nd(2)), Ln(NO(3))(3)L(2) ·nEtOH (Sm(3), Eu(4)), and Ln(NO(3))(3)L(2) (Dy(5), Er(6), Lu(7)). These have been characterized by elemental analysis, infrared and NMR((1)H, (13)C and (31)P) spectroscopy and single-crystal X-ray diffraction. The structures show L to be positioned on opposite sides of the metal with the nitrates forming an equatorial band. When Ln = Dy, Er, and Lu two distinct molecules are present in the unit cell. A major isomer (70%) has a (P)O-Ln-O(P) angle of less than 180° with one of the nitrate ligands twisted out of the plane of the other nitrates while the lower abundance isomer is more symmetric with the (P)O-Ln-O(P) angle of 180° and the nitrate ligands coplanar giving a hexagonal bipyramidal geometry. These isomers cannot be observed by variable temperature solution (31)P NMR measurements but are clearly seen in the solid-state NMR spectrum of the Lu complex. Variable temperature solid-state NMR indicates that the isomers do not interconvert at temperatures up to 100 °C. Attempts to prepare cationic species [Ln(NO(3))(2)L(3)](+)[PF(6)](-) have not been totally successful and led to the isolation of crystals of Lu(NO(3))(3)L(2) and Tb(NO(3))(3)L(2).CH(3)CN (8).

Synthesis, structure and stability of complexes of lanthanide nitrates with [(MeO)2P(O)]2C(OH)Ph and the isomeric (MeO)2P(O)OCHPhP(O)(OMe)2

Abstract The syntheses of compounds Ln(NO3)3L2 (A1–A12) and Ln(NO3)3L′2 (B1–B12), where L[(MeO)2P(O)]2C(OH)Ph and L′(MeO)2P(O)OCHPhP(O)(OMe)2 and LnLaLu except Pm, Tb and Tm, are described. For the heavier lanthanides isomerisation of A to B occurs readily in solution. All compounds are prone to loss of methyl nitrate above ambient temperature, the propensity for this reaction increasing with the atomic weight of the metal. Study by IR and NMR spectroscopies indicate that both the series A and B show slight differences in structure between the heavier and lighter lanthanides and that these differences are probably due to changes in the coordination of the nitrate ligands. The X-ray structures of two isomeric praseodymium complexes A3 (R′=0.0690 for 5326 diffractometer observed reflections) and B3 (R′=0.0393 for 4427 diffractometer observed reflections) show that in both cases the metals are ten-coordinated. The hydrogen atoms of the OH group in A3 were not located but appear to be hydrogen bonded to two of the nitrate groups. One of the ligands in A3 is distorted towards the structure of the isomer. The isomerisations of complexes A to B are discussed in terms of the electrostatic interactions between the phosphorus atoms and the metal centre.

Synthesis of cerium(III) and (IV) complexes of phenacyldiphenylphosphine oxide. The structure of Ce(NO3)3[Ph2P(O)CH2C(O)Ph]3

Abstract The complexes Ce(NO 3 ) 3 (HL) 3 ( I ) and Ce(NO 3 ) 3 L(HL) ( II ) have been prepared where HL = Ph 2 P(O)CH 2 C(O)Ph. The structure of I has been determined and shows that the cerium atom is ten coordinate. HL is bound as both bidentate and monodentate ligands with the third ligand showing intermediate bonding characteristics. The infrared spectra of the complex are discussed in terms of the observed modes of bonding. The thermally unstable Ce(IV) complex, II , contains the phosphine oxide bound as both neutral and anionic chelates, probably in a ten- coordinate complex.

Synthesis of chelate stabilised alcohol– and alkoxo–platinum(II) complexes. X-Ray crystal structure of [Pt(PPh2CH2CMe2O)2]·3.5H2O

Reaction of the new phosphine PPh2CH2CMe2OH with platinum(II) chloro complexes gives complexes of formula [PtCl2(PPh2CH2CMe2OH)2]. The cis isomer in CDCl3 or CD3OD solution is in the ionic, chelate form cis-[[graphic omitted]H)(PPh2CH2CMe2OH)]Cl. At +25 °C, rapid intramolecular –OH exchange takes place. Addition of AgClO4 gives the bis-chelate cis-[[graphic omitted]H)2][ClO4]2. Both of these cis species can be readily deprotonated to give the very stable bis(alkoxo) complex [[graphic omitted])2]. The X-ray structure of this bis(alkoxo) complex as its 3.5H2O solvate has been determined {R= 0.029 for 3 914 observed [I/σ(I) 3.0] diffractometer-collected reflections}. The Pt atom has square-planar co-ordination, with Pt–O bonds of normal length [average 2.024(3)A]. Thus the general instability of alkoxoplatinum complexes is attributed to facile β-hydride elimination and not to abnormally long and weak Pt–O bonds. The trans isomer forms the fluxional chelate complex trans-[[graphic omitted]H)(PPh2CH2CMe2OH)]Cl in CD3OD, but in CDCl3 it gives a neutral non-chelated species. It is also deprotonated by NEt3 but only to the non-fluxional mono-alkoxo complex [[graphic omitted])(PPh2CH2CMe2OH)]. The 31P-{1H} and 1H n.m.r. data for the complexes are discussed.

Complexes of (EtO)2P(O)CH2P(O)(OEt)2 with lanthanide nitrates

The preparation of complexes of (EtO)2P(O)CH2P(O)(OEt)2 = L, with lanthanide nitrates is described. Stable complexes with composition LnL2(NO3)3 can be isolated for Ln = La–Eu and fully characterised. For Ln = Gd–Lu solid compounds could not be isolated. Conductivity and 31P NMR spectroscopy indicate structural changes in solution between the lighter and heavier lanthanides and, whilst electrospray mass spectrometry confirms a dramatic difference in behaviour with complexes of the heavier lanthanides readily decomposing via loss of EtNO3, other experiments show that this does not occur under the conditions of complex formation. The single crystal X-ray structures for Ln = La and Sm show the nitrates and OEt groups to be in close proximity. The changes in spectroscopic properties correlate well with the difficulties in isolating the complexes of heavier metals, and are possibly due to the formation of dimeric complexes rather than loss of ethyl nitrate.

Water soluble platinum(II) and palladium(II) complexes of alkyl sulfonated phosphines

Abstract The reactions of the alkylsulfonated phosphines LM=Ph 2 P(CH 2 ) n SO 3 Na/K ( n =2, 3, 4) with K 2 PtCl 4 and K 2 PdCl 4 have been studied in homogeneous aqueous solution as a function of pH. In homogeneous acidic solution the protonated phosphines react to give cis - and trans -PtCl 2 (LH) 2 . The biphasic reaction between 1,5-cyclooctadiene platinum(II) chloride in dichloromethane and acidified aqueous LNa/K gives a higher proportion of the cis isomer. In neutral solution the initial reaction to give [PtCl(LNa/K) 3 ] + Cl − is followed by slow formation of cis -PtCl 2 (LNa/K) 2 . K 2 PdCl 4 reacts more rapidly to give PdCl 2 (LNa/K) 2 . In homogeneous alkaline solution rapid oxidation of the phosphine occurs with only small amounts of platinum complex being observable. The biphasic reaction yields phosphine oxide in the aqueous layer and a small amount of the chelate complexes PtL 2 in the organic. Representative complexes have been isolated and characterised and the mechanisms for the reactions discussed. The electrospray mass spectra of solutions of the isolated complexes have been recorded in both positive and negative ionisation modes. The positive ionisation spectra are complicated, but platinum and palladium containing ions derived from loss of chloride, H + and HCl are observed in the negative ionisation spectra.