Monodentate P-donor Research Articles

Stereoisomers of Pt(PL)2Cl2 derivatives – structural aspects

AbstractThe coordination complexes of Pt(PL)2Cl2type (PL = monodentate P-donor ligands) cover almost 260 examples as shown by a recent survey covering the crystallographic and structural data. About 20% of these complexes exist as isomers and are summarized in this review. Included are distortion (58.5%),cis-,trans- (37.8%) and mixed isomerism (cis-,trans- and distortion) (3.7%). Distortion isomers, differing by degree of distortion in Pt-L and L-Pt-L angles, are the most common. For these derivatives the most commoncis- arranged with 31 examples and 22 examples withtrans- arranged. The complexes withcis-configuration are more distorted than theirtrans-partners, with the comprehensive values of Pt-L bond distances: 2.246 Å (P) and 2.350 Å (Cl). Such values in the complexes withtrans-configurations are 2.323 Å (P) and 2.308 Å (Cl), respectively. These are discussed with attention to anytrans-influence.

Synthesis and characterization of tetracarbonylmolybdenum(0) and pentacarbonyltungsten(0) complexes of TADDOL-derived, monodentate P-donor ligands

TADDOL-derived P-donor ligands are of interest as ligands in transition metal catalyzed transformations; however, few studies have been conducted on the steric and electronic properties of P-donor ligands derived from TADDOL. To gain more insight into these properties four tetracarbonylmolybdenum(0) and two pentacarbonyltungsten(0) complexes of monodentate P-donor ligands derived from TADDOL have been studied. These studies show that exchanging the chloro substituent on the phosphorus for OMe increases the donor ability of the ligand and that the cis-tetracarbonylmolybdenum(0) complex of the ligand having the OMe substituent spontaneously isomerizes in solution. X-ray crystallographic analyses indicate that the orientations of the 1,3,2-dioxaphosphepane ring and the aryl substituents are not always conserved, even within the same complex.

Setting P-Donor Ligands into Context: An Application of the Ligand Knowledge Base (LKB) Approach

GRAPHICAL ABSTRACT

Oxidatively Induced P–O Bond Formation through Reductive Coupling between Phosphido and Acetylacetonate, 8-Hydroxyquinolinate, and Picolinate Groups

The dinuclear anionic complexes [NBu4][(RF)2M(II)(μ-PPh2)2M'(II)(N(^)O)] (RF = C6F5. N(^)O = 8-hydroxyquinolinate, hq; M = M' = Pt 1; Pd 2; M = Pt, M' = Pd, 3. N(^)O = o-picolinate, pic; M = Pt, M' = Pt, 4; Pd, 5) are synthesized from the tetranuclear [NBu4]2[{(RF)2Pt(μ-PPh2)2M(μ-Cl)}2] by the elimination of the bridging Cl as AgCl in acetone, and coordination of the corresponding N,O-donor ligand (1, 4, and 5) or connecting the fragments "cis-[(RF)2M(μ-PPh2)2](2-)" and "M'(N(^)O)" (2 and 3). The electrochemical oxidation of the anionic complexes 1-5 occurring under HRMS(+) conditions gave the cations [(RF)2M(μ-PPh2)2M'(N(^)O)](+), presumably endowed with a M(III),M'(III) core. The oxidative addition of I2 to the 8-hydroxyquinolinate complexes 1-3 triggers a reductive coupling between a PPh2 bridging ligand and the N,O-donor chelate ligand with formation of a P-O bond and ends up in complexes of platinum(II) or palladium(II) of formula [(RF)2M(II)(μ-I)(μ-PPh2)M'(II)(P,N-PPh2hq)], M = M' = Pt 7, Pd 8; M = Pt, M' = Pd, 9. Complexes 7-9 show a new Ph2P-OC9H6N (Ph2P-hq) ligand bonded to the metal center in a P,N-chelate mode. Analogously, the addition of I2 to solutions of the o-picolinate complexes 4 and 5 causes the reductive coupling between a PPh2 bridging ligand and the starting N,O-donor chelate ligand with formation of a P-O bond, forming Ph2P-OC6H4NO (Ph2P-pic). In these cases, the isolated derivatives [NBu4][(Ph2P-pic)(RF)Pt(II)(μ-I)(μ-PPh2)M(II)(RF)I] (M = Pt 10, Pd 11) are anionic, as a consequence of the coordination of the resulting new phosphane ligand (Ph2P-pic) as monodentate P-donor, and a terminal iodo group to the M atom. The oxidative addition of I2 to [NBu4][(RF)2Pt(II)(μ-PPh2)2Pt(II)(acac)] (6) (acac = acetylacetonate) also results in a reductive coupling between the diphenylphosphanido and the acetylacetonate ligand with formation of a P-O bond and synthesis of the complex [NBu4][(RF)2Pt(II)(μ-I)(μ-PPh2)Pt(II)(Ph2P-acac)I] (12). The transformations of the starting complexes into the products containing the P-O ligands passes through mixed valence M(II),M'(IV) intermediates which were detected, for M = M' = Pt, by spectroscopic and spectrometric measurements.

Dibenzo[b,f]phosphepines: Novel Phosphane–Olefin Ligands for Transition Metals

New, stable heterobidentate phosphane–olefin ligands based on the dibenzo[b,f]phosphepine backbone are reported together with their redox properties and coordination chemistry to rhodium(I). The X-ray crystal structures and DFT calculations show different conformations for the P-phenyl (6a) and P-mesityl (6b) derivatives. Cyclic voltammetry (vs Fc/Fc+) of 6a supported by UV–vis spectroelectrochemistry showed two cathodic waves, a reversible one at E1/2 = −2.62 V (If/Ib = 1.0) and a quasi-reversible (If/Ib ≈ 1.2) one at E1/2 = −3.03 V. Reduction with sodium afforded a mixture of the radical anion [6a•]−, characterized by EPR spectroscopy, and dianion [6a]2–, for which an X-ray crystal structure was obtained. Both 6a and 6b bind to RhI centers, giving rise to 3:1 (8a) and 2:1 (8b) ligand:Rh complexes, respectively. Two dibenzo[b,f]phosphepines in 8a and 8b act as heterobidentate ligands in which both the phosphorus atom and the olefinic double bond coordinate to rhodium, but the third ligand in 8a binds as a monodentate P-donor. The cyclic voltammogram of 8b showed two close-lying waves, a one-electron reversible wave at −1.45 V and a two-electron quasi-reversible wave at −1.80 V (If/Ib ≈ 1.3). 8a showed a reversible wave at −1.71 V and irreversible waves at lower potentials.

Preparation, Crystal Structures, and Behavior in Solution of Cobalt(III) Complexes Containing 2-Cyanoethylphosphines: trans-[Co(Me2dtc)2{P(CH2CH2CN)nPh3−n}]BF4 (n = 1–3; Me2dtc−: N,N-Dimethyldithiocarbamate)

Abstract A series of cobalt(III) complexes containing 2-cyanoethylphosphines, [Co(Me2dtc)2{P(CH2CH2CN)nPh3−n}2]BF4 {Me2dtc−: N,N-dimethyldithiocarbamate; n = 1 (1), 2 (2), and 3 (3)} have been prepared, and their molecular structures in the crystals and in solution have been characterized. X-ray analysis revealed that all complexes isolated as single-crystals were the trans-isomers. The Co–P bond lengths for the 2-cyanoethylphosphines in complexes 1–3 are almost invariant to the number of 2-cyanoethyl substituent groups. Unlike related complexes with other monodentate P-donor ligands, complexes 1–3 in solution showed dissociation and isomerization equilibriums, which were achieved immediately after dissolving the crystals. These characteristic features of the complexes would result from the weak σ-donor and π-acceptor abilities of 2-cyanoethylphosphines. Furthermore, mixing of complex 1 and NaN3 in acetonitrile gave cis-[Co(Me2dtc)2(N3){P(CH2CH2CN)Ph2}] quantitatively, and refluxing the mixture resulted in the phosphine–tetrazolate complex, [Co(Me2dtc)2(Ph2PCH2CH2CN4-κ2P,N1)] (4).

Neutral η6-arene ruthenium complexes with monodentate P-donor ligands: Activation in the transfer hydrogenation reaction

Five Ru(II) neutral complexes C of the type [RuCl2(η6-arene)(P)] (P=monodentate phosphorus ligand) have been prepared: C1 (arene=p-cymene, P=PPh3); C2 (arene=p-cymene, P=(R)-Monophos); C3 (arene=p-cymene, P=(S)-Ph-Binepine); C4 (arene=benzene, P=PPh3); and C5 (arene=benzene, P=(S)-Ph-Binepine). These complexes have been screened as catalytic precursors in the transfer hydrogenation of acetophenone with 2-propanol. Under optimised conditions at 82°C complexes C1 and C4 provide full conversion in less than 20min at a [Ru]:substrate ratio of 1:200. With the chiral complexes C2 and C3 good TOF values have been reached but with low enantioselectivities. The activation of the catalytic precursor has been studied. Based on NMR evidence, a mechanism in which the catalytically active species is a Ru monohydride complex arising from the reaction of the catalyst precursor C with 2-propanol in the presence of a base is suggested. The reaction shows different sensitivity towards excess of phosphine: whereas excess of PPh3 slows down the reaction severely, excess of (S)-Ph-Binepine does not cause such a sharp effect. An excess of chloride ion affects the activation of the precursor C.

P-donor ligand containing ruthenium half-sandwich complexes as protein kinase inhibitors

Metal complexes have emerged as promising and novel scaffolds for the design of enzyme inhibitors. Reported herein are the design, synthesis, and evaluation of protein kinase inhibition properties of pyridocarbazole half-sandwich complexes containing P-donor ligands. The nature of the monodentate P-donor ligand has a strong effect on protein kinase binding properties, most likely due to a direct interaction with the glycine-rich loop in the ATP-binding site. We furthermore discovered that PMe 3 pyridocarbazole complexes are interesting lead structures for the design of potent inhibitors for the protein kinase TrkA for which we obtained a nanomolar organometallic inhibitor.

Expansion of the Ligand Knowledge Base for Monodentate P-Donor Ligands (LKB-P)

We have expanded the ligand knowledge base for monodentate P-donor ligands (LKB-P, Chem. Eur. J. 2006, 12, 291−302) by 287 ligands and added descriptors derived from computational results on a gold complex [AuClL]. This expansion to 348 ligands captures known ligand space for this class of monodentate two-electron donor ligands well, and we have used principal component analysis (PCA) of the descriptors to derive an improved map of ligand space. Potential applications of this map, including the visualization of ligand similarities/differences and trends in experimental data, as well as the design of ligand test sets for high-throughput screening and the identification of ligands for reaction optimization, are discussed. Descriptors of ligand properties can also be used in regression models for the interpretation and prediction of available response data, and here we explore such models for both experimental and calculated data, highlighting the advantages of large training sets that sample ligand space well.

Expanding the scope of atropisomeric monodentate P-donor ligands in asymmetric catalysis. Asymmetric allylic alkylation of 1,3-diphenylpropenyl-1-esters by Pd/BINEPINE catalysts

Monodentate binaphthophosphepines (BINEPINES) have been tested in the palladium-catalyzed asymmetric allylic alkylation of 1,3-diphenylallyl esters. Stereoselectivities of up to 92% ee have been achieved in the alkylation of the acetate ester with the C-nucleophile, generated in situ by the action of BSA ( N, O-bis(trimethylsilyl)acetamide) on dimethylmalonate in the presence of a catalytic amount of sodium acetate.

Rhodium(I) complexes of α-keto-stabilised 1,2-bis(diphenylphosphino)alkane mono ylides

Rhodium(I) complexes of the hybrid ylide-phosphine ligands, $Ph_2P(CH_2)_nPPh_2(CHC(O)C_6H_5)$ (n = 1: dppm-yl, or 2: dppe-yl) have been synthesized from $[Rh(\mu-Cl)(COD)]_2$ (COD = 1,5-cyclooctadiene) and characterized by NMR spectroscopic and X-ray structural methods. The dppe-yl behaves as an ambidentate ligand; it functions as a monodentate P-donor ligand with a dangling ylidic carbon in the neutral chloro complex, [(COD)Rh(Cl)(dppe-yl)] (1), whereas replacement of the chloride by a non-coordinating counter anion results in the formation of the complexes, $[(COD)Rh(L-L')]^+$ (L-L' = dppe-yl (2) or dppm-yl (3)) respectively in which the ligands are bonded to the metal via the phosphorus and the ylidic carbon atoms. The 1,5- cyclooctadiene (COD), present in the Rh(I) precursor, remains intact in the products. The structures of 1, 2 and 3 have been confirmed by X-ray crystallography.

Use of Intraligand CH Coupling Constants to Assess Binding in Organometallic Compounds. Insight into Electronic and Steric Properties of Monodentate P-Donor Ligands

In a series of methylcobaloximes (LCo(DH)2CH3, where DH = monoanion of dimethylglyoxime), the influence of P-donor ligands (L) on 1JCH values of the Co−CH3 moiety correlated well with the pKa of L except when L was bulky (Cy3P and i-Pr3P). In contrast, no single steric parameter of those known for the trivalent P donors examined could be used to describe the variance of 1JCH. The results indicate that the dominant property of L influencing this 1JCH is electron donation. Although poor, the best correlation with a steric parameter was found with calculated cone angles (CCA) determined by experimental methods on methanol-coordinated cobaloximes. Since the single parameter fits with pKa indicated a steric effect, multiparameter regressions were performed using various combinations of electronic and steric terms. Terms reflecting only σ-donor ability (e.g., pKa) gave better correlations than terms reflecting combinations of σ-donor and π-acceptor properties (e.g., Σχ). CCA values also resulted in better multiparameter fits of the data than other reported steric terms. Using a multiparameter approach also allowed for the simultaneous fit of data for L = phosphine and phosphite ligands. Correlations of this type were poor with single parameter fits. The sensitivity of 1JCH to trans ligand electronic and steric effects indicates that small changes in the hybridization of the Co−CH3 moiety occur. This method allows us to probe the nature of Co−C bonding in the ground state. The other experimental methods for probing this bond (e.g., X-ray crystallography, FT-Raman spectroscopy, etc.) indicate that this bond is relatively insensitive to the trans ligand in the ground state. Thus, 1JCH values may be a useful general method for examining B12 systems and also hold promise for other types of organometallic compounds.

Steric effects of the 2-(diphenylphosphino)pyridine bridging ligand in the synthesis of binuclear palladium( II) complexes

Treatment of [Pd{CH 2C(CH 3)CH 2}(Ph 2PPy)Cl] (Ph 2PPy = 2-(diphenylphosphino)pyridine) with cis-[Pd( tBuNC) 2Cl 2] in dichloromethane affords the mixed isocyanide-tertiary phosphine complex cis-[Pd( tBuNC)Ph 2PPy)Cl 2], in which the Ph 2PPy is a monodentate P-donor, and [{Pd[CH 2C(CH 3)CH 2]Cl} 2]. The steric effects of the Ph 2PPy bridging ligand in determining the reaction course is discussed. The complex cis-[Pd( tBuNC)(Ph 2PPy)Cl 2] was crystallographically characterized: P2 1/ n, a = 15.143(2), b = 9.527(1), c = 17.517(4) Å, β = 113.96(1)°, V= 2309.4(7) Å 3, Z = 4. The final R value was 0.044, R w = 0.046 for the 3078 reflections with I > 3σ( I).

Double deprotonation of ruthenium(II) cations containing 1,2-dimethyl-substituted .eta.6-arenes. Protonation of the resulting exo-coordinated (o-xylylene)ruthenium(0) complexes and x-ray crystal structures of the agostic (.eta.3-pentamethylbenzyl)ruthenium(II) complexes [Ru{.eta.3-(HCH2)(CH2)C6Me4}{(Z)-Ph2PCH:CHPPh2}(PMe2Ph)]PF6 and [Ru{.eta.3-(HCH2)(CH2)C6Me4}(PMe2Ph)3]PF6

Treatment of the various ruthenium(II) salts [Ru(ONO2)(eta-6-1,2-dimethylarene)L2]NO3 and [Ru(O2CCF3)(eta-6-1,2-dimethylarene)L2]PF6 with KO-t-Bu or (Me3Si)2NNa in the presence of a ligand L' gives o-xylylene (o-quinodimethane) complexes of zerovalent ruthenium, i.e. Ru{eta-4-(CH2)2C6Me4}L2L' (L = L' = PMe2Ph, P(CD3)2Ph, PMePh2, P(OMe)3, P(OCH2)3CMe; L2 = Ph2PCH2CH2PPh2, L' = PMe2Ph; L2 = (Z)-Ph2PCH=CHPPh2, L' = PMe2Ph, P(CD3)2Ph), Ru{eta-4-(CH2)2C6H2Me2}L2L' (L = L' = PMe2Ph, PMePh2), and Ru{eta-4-(CH2)2C6H4}(PMe2Ph)3, in good to moderate yields. In all cases the o-xylylene group is coordinated through its exo pair of double bonds. The reactions are proposed to proceed via the undetected intermediates Ru(o-xylylene)L2 (L = monodentate P-donor ligand, L2 = bidentate P-donor ligand) in which the ruthenium atom can migrate from the endo to the exo pair of double bonds before ligand L' attacks. On treatment with HPF6, Ru{eta-4-(CH2)2C6Me4}L2L' and Ru(eta-4-(CH2)2C6H4}(PMe2Ph)3 give (eta-3-benzyl)ruthenium(II) salts [Ru{eta-3-(HCH2)(CH2)C6Me4}L2L']PF6 (L = Ph2PCH2CH2PPh2, L' = PMe2Ph (1); L = (Z)-Ph2PCH=CHPPh2, L' = PMe2Ph (2), P(CD3)2Ph (2a); L = L' = PMe2Ph (3), P(CD3)2Ph (3a)) and [Ru{eta-3-(HCH2)-(CH2)C6H4}(PMe2Ph)3]PF6 (4) in which the added proton bridges the metal atom and a terminal methylene group. Crystals of 2 are monoclinic, space group P2(1)/n, with a = 18.88.4 (3) angstrom, b = 18.612 (3) angstrom, c = 12.361 (1) angstrom, beta = 90.40 (1)-degrees, and Z = 4; those of 3 are monoclinic, space group C2/c, with a = 21.220 (8) angstrom, b = 23.412 (10) angstrom, c = 18.580 (7) angstrom, beta = 126.05 (1)-degrees, and Z = 8. The structures were solved by heavy-atom methods and refined by least-squares analysis to R = 0.042 and R(w) = 0.053 for 5787 independent reflections (I greater-than-or-equal-to 3-sigma) (2) and R = 0.053 and R(w) = 0.076 for 5832 independent reflections (I > 3-sigma) (3). Both cations contain a ruthenium atom coordinated in a distorted-octahedral arrangement by a eta-3-pentamethylbenzyl group, which occupies two sites, three phosphorus atoms, and an agostic methyl hydrogen atom that has been directly located in 2 but not 3. The eta-3-benzyl interaction in 2 shows the usual asymmetry, the shortest Ru-C bond being to the terminal CH2 group (Ru-C(22) = 2.164 (5) angstrom, Ru-C(2) = 2.342 (4) angstrom, Ru-C(1) = 2.358 (4) angstrom). The metrical parameters defining the agostic Ru-H-CH2 interaction in 2 are r(Ru-C) = 2.416 (5) angstrom, r(Ru-H) = 1.92 (4) angstrom, r(C-H) = 1.01 (5) angstrom, and angle C-H-Ru = 107 (3)-degrees. The distances from ruthenium to the terminal carbon atoms in 3 (Ru-C(11) = 2.333 (9) angstrom, Ru-C(22) = 2.283 (10) angstrom) are almost equal within experimental error, in contrast with the corresponding distances in 2, and indicate that the solid-state structure of 3 is an average in which either C(11) or C(22) is protonated. Variable-temperature NMR (H-1, P-31) spectra of complexes 1, 2, 2a, 3, 3a, and 4 show these molecules to be fluxional as a consequence of three processes: (1) reversible Ru-H (agostic) bond breaking, which cannot be frozen out, even at -100-degrees-C; (2) reversible eta-3 reversible eta-1 interconversions of the benzyl group, for which the estimated DELTA-G(double dagger) values are ca. 13 kcal/mol at 303 K for 2 and ca.

Perhalophenyl complexes of palladium(II) containing keto-stabilized phosphorus ylides of the type Ph 2P(CH 2) nPPh 2CHC(O)R

From suitable perhalophenyl derivatives of palladium(II), viz.: Pd(C 6F 5) 2-(SC 4H 8) 2, [Pd(μ-X′) (C 6X 5) 2] 2(NBu 4) 2, [Pd(μ-Cl)(C 6X 5)(SC 4H 8)] 2 (X = F, Cl, X′ = Cl, Br), new complexes of various types have been prepared, viz.: trans-Pd(C 6F 5) 2(Y) 2, Pd(C 6X 5) 2(Y), PdCl(C 6X 5)(Y) (X = F, Cl). The neutral ligand Y is a keto-stabilized phosphorus ylide of the type Ph 2P(CH 2) n PPh 2CHC(O)R ( n = 1, R = CH 3, C 6H 5; n = 2, R = C 6H 5) acting in a terminal monodentate P-donor or a bidentate chelate P,C-donor mode. The reaction of PdCl(C 6F 5)(Y) complexes with HCl leads to the corresponding PdCl 2(C 6F 5)(YH) complexes in which the phosphonium cation [YH] + behaves as monodentate P-donor at its phosphinic end. IR and 31P NMR spectroscopy were used to decide the coordination mode of the ligands and, in some cases, to reveal the presence of two isomers.

Synthesis and characterization of mercury(II) complexes with diphenylphosphineacetic acid

Complexes of divalent mercury with diphenylphosphineacetic acid (HA) of the composition HgX2(HA)2, HgX2(HA), HgX(A) (HA), HgA2 and Na2HgA4 (X = Cl, Br, I) were synthesized and characterized by means of spectroscopic and further techniques in the solid state and in solution. The coordination environment of mercury is constituted by halides and/or phosphine ligands in tetrahedral arrangement. HA acts as a monodentate P-donor, the A- anion either as a monodentate P-donor (in Na2HgA4) or as a chelating P,O-donot (in the remaining cases).

Synthese und reaktivität von dienylmetall-verbindungen: XI. Zur koordination bifunktioneller liganden des typs R 2P(CH 2) nAsR 2 in cyclopentadienylnickel-komplexen

Zusammenfassung Diphenylphosphino(diphenylarsino)alkylidenes R 2 P(CH 2 ) n AsR 2 (LL, R = C 6 H 5 , n = 1, 2) form the complexes [C 5 H 5 Ni(LL)]X, [C 5 H 5 Ni(LL) 2 ]X and C 5 H 5 Ni(LL)X. In stable compounds, R 2 PCH 2 AsR 2 acts as a monodentate P-donor ligand only.

Complexes of divalent platinum with diphenylphosphineacetic acid

Diphenylphosphineacetic acid (HA) acts as a monodentate P-donor towards divalent platinum; the anion acts as a bidentate P,O-donor. Three types of complexes have been prepared, PtX2(HA)2, PtXA(HA) and PtA2 (X = Cl, Br, I, SCN), whose formation is determined primarily by the type of X, the acidity of the medium and the polarity of the solvent. It follows from electronic, infrared and 31P-NMR spectra that all the prepared complexes are cis-square planar in structure.