Robert W. Hilts

Coordination chemistry of unsaturated cyclic and acyclic PNS and PNSe ligands

Abstract This review is primarily concerned with the synthesis, structure and fluxional behaviour of cyclic and acyclic chalcogen-nitrogen systems containing phosphorus (V) or phosphorus (III). The cyclic Ph 4 P 2 N 4 S 2 R − and Ph 4 P 2 N 4 S 2− 2 anions (and their selenium analogues) are versatile ligands for both early and late transition metals. Mono-, di-, tri- and tetradentate bonding modes have been established for the eight-membered P 2 N 4 S 2 ring in these inorganic heterocycles. Ligation occurs through sulphur (or selenium) and/or nitrogen, while the coordinatively saturated phosphorus (V) centres serve as an informative probe of fluxional processes. By contrast, coordination occurs exclusively through phosphorus in both the cyclic and acyclic phosphorus (III) systems. In order to provide a background for the discussion of the coordination chemistry of hybrid Pue5f8N/Sue5f8N systems, the review begins with a short account of N-bonded complexes of cyclophosphazenes and S 4 N 4 , which is followed by a discussion of metal complexes of the S 4 N 2− 4 dianion. The concluding section of the review describes metal complexes of some related anionic Sue5f8N ligands. In particular, the alkali metal derivatives of the acyclic [RNS(R′)NR″] − anions and transition metal complexes of the cyclic radical PhCN 2 S 2 are discussed.

Synthesis, Properties, and Bishomoaromaticity of the First Tetrahalogenated Derivative of a 1, 5-Diphosphadithiatetrazocine: A Combined Experimental and Computational Investigation

The first example of a tetrahalogenated derivative of a diphosphadithiatetrazocine, 1,5-Cl(2)P(NSN)(2)PCl(2) (3), was synthesized by cyclocondensation of a 2:1 mixture of SCl(2) and SO(2)Cl(2) with Cl(2)P(NSiMe(3))N(SiMe(3))(2) in CH(2)Cl(2). The heterocycle 3 was isolated as an orange, moisture-sensitive, thermally labile solid and characterized by mass spectrometry, (31)P NMR, and UV-visible spectroscopy. The low-field (31)P NMR chemical shift (93.7 ppm) is indicative of a cross-ring S-S interaction in the eight-membered P(2)N(4)S(2) ring, and this conclusion is supported by density-functional computations. Compound 3 exhibits unusual physical properties compared with those of the known tetraalkyl or aryl derivatives; mild heating (90 degrees C) produces an orange rubbery material. The bishomoaromatic character of the diphosphadithiatetrazocine 1,5-R(2)P(NSN)(2)PR(2) (R = Me, Cl, F) is evinced by the negative nucleus-independent chemical shift (NICS) values, and the through-space bishomoconjugation in the eight-membered ring decreases with increasing electronegativity of the substituents attached to the P atoms.

Dalton communications. Preparation, crystal structure and fluxional behaviour of σ-S-bonded palladium and platinum complexes of the Ph4P2N4S2R–(R = Me or But) anions

The reaction of the Ph4P2N4S2R– anions (R = Me or But), generated from 1,5-Ph4P2N4S2 and the appropriate alkyllithium reagent, with cis- or trans-[MCl2(PEt3)2](M = Pd or Pt) produces the complexes [MCl(PEt3)2(Ph4P2N4S2R)](R = Me, M = Pd or Pt; R = But, M = Pt) shown by X-ray crystallography (M = Pd, R = Me) to involve σ-S bonding of the P2N4S2 ring to the metal; variable-temperature 31P NMR spectra of these complexes indicate a significant energy barrier to rotation about the M–S bond of 41–46 kJ mol–1.

PREPARATION, SPECTROSCOPIC AND STRUCTURAL CHARACTERIZATION OF ETA-1-N AND ETA-2-SE,SE' COMPLEXES OF A P2N4SE2 RING

The reaction of 1,5-Ph4P2N4Se2, 1, prepared by the treatment of Ph2PN2(SiMe3)3 with a mixture of SeCl4 and Se2Cl2 in acetonitrile, with [PtCl2(PEt3)]2 gives the adducts [PtCl2(PEt3)]n[η1-N-Ph4P2N4Se2](2, n- 1; 3, n- 2) in which the P2N4Se2 ring is shown by an X-ray structural determination of 3 to contain a transannular Se–Se interaction; the oxidative addition of 1 or 2 to Pt(C2H4)(PPh3)2 produces the corresponding η2-Se,Se′ complexes.

Preparation and structure of a ruthenium dicarbonyl derivative of the P2N4S2 ring

The reaction of Ru(CO)4(C2H4) or Ru(CO)5 with 1,5-Ph4P2N4S2 in CH2Cl2/hexane at 23°C produces the dimer [Ru(CO)2(Ph4 P2N4S2)]2 (2), which was shown by X-ray crystallography to have a centrosymmetric structure in which the P2N4S2 ring is attached to one ruthenium atom through two (geminal) nitrogen atoms and the remote sulfur atom and serves as a bridge to the other ruthenium atom via the second sulfur atom. Crystals of 2 ·2(CH2Cl2) are triclinic, space group P1 (No. 2), a = 12.901(1) A, b = 13.072(1) A, c = 10.123(1) A, α = 100.88(1)°, β = 98.90(1)°, γ = 67.50(1)°, V = 1542.4(3) A, Z = 1 with final R and Rw values of 0.040 and 0.027, respectively.

Diphosphadithia- and Diphosphadiselena-Tetrazocines and Their S(Se), S′ (Se′)-dialkyl(aryl)derivatives

Abstract The preparation, structures, 31 P NMR spectra (solution and solid state) and reactions of diphosphadithia- and diphosphadiselenatetrazocines 1, 5-R 4 P 2 N 4 E 2 (E = S, Se) and their E, E′-diorgano derivatives 1, 5-R 4 P 2 N 4 E 2 R′ 2 (R′ = alkyl, aryl) are described. New aspects of the chemistry of the folded eight-membered rings 1, 5-R 4 P 2 N 4 S 2 include (a) the characterization of structural isomers of the type 1, 5 [R(R′)P] 2 N 4 S 2 , (b) the preparation and X-ray structures of metal complexes with η 1 -N, η 2 -S, S′ or η 2 -N, S-μ-S′ bonding modes and the fluxional behaviour of the latter complexes, (c) the generation and reactions of the dianion 1, 5-Ph 4 P 2 N 4 S 2 2- , (d) the fluxional behaviour of the monoanion Ph 4 P 2 N 4 S 2 Me − and (e) the spontaneous polymerization of Cl 4 P 2 N 4 S 2 . The selenium-containing rings exhibit two remarkable differences in behaviour compared to their sulphur analogues: (i) the isomerization of 1, 5-Ph 4 P 2 N 4 Se 2 R 2 (R = Me, Et) into the 1, 3-isomer at 25°C and (ii) the dissociation of 1, 5-Ph 4 P 2 N 4 Se 2 into Ph 2 PN 2 Se· radicals in CH 2 Cl 2 .

S,S-Diorgano Derivatives of the P2N4S2 Ring

Abstract The reaction of [Li(Ph4P2N4S2R)THF]2 with alkyl iodides R′I produces the msymmetrically substituted derivatives Ph4P2N4(SR)(SR′) as lithium iodide adducts. The coordinated LiI is readily removed in CH3CN or CH2Cl2 to give the eight-membered rings in a boat conformation (∂ 31P = 14–17 ppm). The boat conformers readily isomerize to the corresponding chair somers (∂ 31P = 25–29 ppm) upon gentle heating.

Early Transition-Metal Complexes of Phosphorus-Nitrogen-Sulfur Heterocycles

Abstract The preparation, structural characterization and some synthetic applications of the first early transition-metal complexes of the P2N4S2 ring are presented.

New Macrocyclic Ligands with P2N4S2 Rings in the Framework

Abstract Several new macromolecules containing two Ph4P2N4S2 rings linked by meta-xylyl groups have been prepared.