John Malito

Cyclometallation of trimesitylphosphine

Abstract Synthetic and spectral ( 1 H, 13 C and 31 P NMR) details are presented for the formation of cyclometallated palladium(II) and platinum(II) dimers by reaction of trimesitylphosphine with MCl 2 and MCl 2 Y 2 (M  Pd, Pt; Y  CH 3 CN, PhCN, 1 2 COD) and for the corresponding halide metathesis products. These dimers are very stable with a strong MC bond. There were no non-cyclometallated products isolated and cyclopalladation is definitely more facile than cycloplatination. The latter two observations are unusual with respect to the known reactivity of phosphines with palladium(II) and platinum(II) centres. Geometric isomerism is observed for the Pt species.

Correlations of carbonyl stretching frequencies and 31P and 95Mo NMR parameters for FAC-[Mo(CO)3(bipy)(PR3)] complexes

Abstract Several complexes of the type [Mo(CO) 3 (bipy)(PR 3 )] [where bipy = 2,2′-dipyridine, R = n -Bu, Me, p -C 6 H 4 -X; X = F, Cl, H, CH 3 , OCH 3 , N(CH 3 ) 2 ] were synthesized and characterized by 31 P NMR, 95 Mo NMR and IR spectroscopy. Relationships are drawn between the bonding nature of the ligands and the 95 Mo and 31 P NMR chemical shifts and the v (CO) values. Correlations of δ( 95 Mo), Δδ( 31 P) and v (CO) to various parameters such as ligand p K a , ligand cone angle θ, and the Kabachnik parameter (σσo) are discussed and indicate the interrelationship of the donor abilities of CO, dipy and the phosphine ligands. The importance of steric effects in influencing net metal electron density is demonstrated by the results.

A 31P NMR solution study of LnAuCl. Comparison of triphenylphosphine and 5-phenyldibenzophosphole ligands

Variable-temperature solution 31P NMR measurements for LAuCl+L [L = 5-phenyldibenzophosphole (PhDBP) and triphenylphosphine (Ph3P)] systems allow for assignments for several LnAuCl species (n = 1, 4; L = PhDBP and n = 1–4, L = Ph3P). Generally, the Ph3P species are more kinetically labile than the PhDBP species, but both systems show fast exchange processes even at low (183 K) temperatures. Similar measurements for the systems LAuCl+L′ allow for assignments for the mixed species [(PhDBP)4-n(Ph3P)nAu]Cl and, possibly, (PhDBP)(Ph3P)AuCl. The ligands Ph3P and PhDBP tend to stabilize low- and high-coordinate species, respectively, which is rationalized on the basis of both the steric and electronic properties of these two ligands.

MOLYBDENUM-95 NMR CHEMICAL SHIFTS OF SOME MOLYBDENUM CARBONYLATE ANIONS

Abstract Molybdenum-95 NMR chemical shifts are reported for a range of molybdenum(0) carbonylate anions of the type [Mo(CO)5X]− formed by warning dimethylsulfoxide solutions of molybdenum hexacarbonyl and alkali metal hydroxide, halide and pseudohalides. The chemical shift values extend over a thousand ppm and reflect the importance of ligand field strength, polarizability and electronegativity factors in determining the Mo-95 chemical shifts; the ‘normal halogen dependence’ is confirmed for these d6 species. The decreasing shielding effects of the coordinated anions in the [Mo(CO)5X]- complexes is in the order H− > CN− > I− > NCO− > NCS− > NCSe− > Br− > N3− > NO2− > Cl− > O2CH− > O2N− > OCH3− > F−.

A 95Mo NMR study of electronic effects in tetracarbonyl−molybdenum complexes of aromatic α-diimine chelate ligands

Abstract Studies of nine (α-diimine)MO(CO) 4 complexes demonstrate the importance of metal-to-ligand charge-transfer contributions for the chemical shift in 95 Mo NMR spectroscopy. The δ( 95 Mo) values, which occur in the range − 847 to − 1164 ppm, correlate with the calculated LUMO coefficients c N 2 at the coordinating (chelate) nitrogen centres, with the McLachlan π-spin populations p N ML and with ESR coupling constants a ( 14 N) of the anion radical complexes.

STERIC AND ELECTRONIC DESTABILIZATION OF THE P—Se BOND IN TRIARYLPHOSPHINE SELENIDE SYSTEMS

Abstract Electronic and steric effects in SeP(Ar), compounds are discussed with the assistance of 1J(77Se-31P) correlations with d(P—Se) values and the pKa of the arylphosphines.

Non-Metal Derivatives of the Bulkiest Known Tertiary Phosphine, Trimesitylphosphine

Abstract Trimesitylphosphine (Pmes3) is the bulkiest known tertiary phosphine. The low yield synthesis of this known compound, its failure to form a carbon disulfide adduct or a selenide derivative, the relatively low values for v(P—O), v(P—S) and v(P—H) in its oxide, sulfide and phosphonium salt respectively, and the high barriers to rotation about the P—Cipso bond in Pmes3, and its derivatives all attest to this fact. Nevertheless, Pmes3, does show chemistry typical of most tertiary phosphines due to its relatively high basicity and the electronic character of even this most bulky phosphine must also be considered in any discussion of its chemistry.

95Mo NMR studies of some carbonylate anions

Abstract 95 Mo NMR chemical shifts are reported for a range of molybdenum(0) carbonylate anions of the type [Mo(CO) 5 X] − (X = halide or pseudohalide). The dimethylsulphoxide solution data substantiate the existence of more than one product, unexpected products and ambidentate pseudohalogen bonding modes. The sensitivity of the 95 Mo NMR chemical shifts to the ligand field and polarizability properties of the anions in the [Mo(CO) 5 X] − complexes results in an over 500 ppm range of values (−1980 to −1435 ppm); the shielding order is H − > C N − > I − > N CO − > N CS − > N CSe − > Br − > N − 3 > N O − 2 > Cl − > O 2 CH − > O 2 N − > O CH − 3 . Species arising from the reaction of Mo(CO) 6 with hydroxide ion have been previously implicated in the homogeneous catalysis of the water-gas shift reaction; the utility of 95 Mo NMR spectroscopy in identifying some of these products is also described.

A correlation of pyridine ligandcis- andtrans-influences in [Pt(Pmes2C6H2Me2CH2)Cl(NC5H4X)]

SummaryThe cycloplatinated species,cis- andtrans-[Pt(Pmes2· C6H2Me2CH2)Cl(NC5H4X)] (X = CN, CO2Me, H, Ph, Me,t-Bu and NMe2), are formed byin situ chloro-bridgecleavage of [Pt(Pmes2C6H2Me2CH2)Cl]2.Cis - andtrans-influences exerted by NC5H4X show apparently exactly opposite correlations with ligand basicities and inverse correlation with each other. High basicity corresponds to strongtrans-influence but weakcis-influence andvice versa. These relationships are rationalized in terms of σ-inductive effects.

Ligand effects in the substitution chemistry of cis-bis(piperidine)tetracarbonylmolybdenum(O). A molybdenum-95 NMR study

Abstract Molybdenum-95 NMR chemical shifts are reported for a series of Mo(O) compounds of the type Mo(CO) 4 (pip) 2− n L n ( n = 1,2; L = substituted pyridine ligands). The σ( 95 Mo) values correlate well with the p K a values for the substituted pyridines; for the n = 1 series, σ ( 95 Mo) ranges from − 1053 ppm (p K a = 1.86 for 4-CN) to − 1120 ppm (p K a = 9.61 for 4-NMe 2 ). The effects of solvent polarity and some in situ reactivity studies are described and the nature of the MoL bond compared to that with piperidine and some other ligands is discussed.