Reactions of [Mo(N2)2(dppe)2] with organic isocyanates

The reactions of [Mo(N₂₂(dppe)₂], (dppe  Ph₂PCH₂CH₂PPh₂) with RC₆H₄NCO (R  H, p-CH₃, p-Cl) in benzene under irradiation produces [Mo(RC₆H₄NCO)₂(dppe)₂] in good yields. Comparison of the infrared data for these complexes, with those previously reported for metal complexes of CO₂-like molecules suggest a η²-C,O coordination to the metal.     

Stepwise reduction of the thiocarbonyl ligand: hydride transfer to CS: thioformyl,thioformaldehyde, methylthiolato,secondary carbene,formyl and iminoformyl complexes of osmium

The complexes OsHX(CS)L(PPh₃)₂ (X  Cl, Br; L  CO and X  Cl; L  CN-p-tolyl), which contain mutually cis hydrido and thiocarbonyl ligands, undergo transfer of the hydrido ligand to CS when treated with CO to give blue complexes containing the thioformyl ligand [OsCHS]. OsCl(CHS)(CO)₂(PPh₃)₂ reacts with borohydride to give the first metal complex of the thioformaldehyde monomer, viz. Os(η²-CH₂S)(CO)₂(PPh₃)₂, which reacts rapidly with HCl to give OsCl(SCH₃)(CO)₂(PPh₃)₂ and then, by a slower reaction, OsCl₂(CO)₂(PPh₃)₂ and CH₃SH. The ligands produced in this stepwise reduction have possible relevance as models for postulated intermediates in the Fischer—Tropsch synthesis. Synthetic routes to formyl [OsCHO], iminoformyl [OsCHNMe] and secondary carbene complexes [OsCHSMe, OsCHNMe₂, OsCHOMe] are also demonstrated.     

The chemistry of hetero-allene and -allylic derivatives with rhodium : I. The reactions of rhodium(I)-hetero-allylic compounds with hetero-allenes; B. Carbon Disulfide

The rhodium(I) complexes Rh[X-C(Z)-Y] (PPh₃)₂, in which [X-C(Z)-Y] represents an uninegative unsaturated heteroallylic bidentate ligand, coordinating via two of the three hetero atoms (X, Y, Z  P, S or N), react at elevated temperature with an excess of the hetero-allene SCS to give the rhodium(I)-thiocarbonyl complexes Rh[X-C(Z)-Z](CS)(PPh₃). In the initial step a first CS₂ molecule is coordinated side-on by one of the CS double bands. Subsequent reactions can be blocked at this stage by addition of pyridine, resulting in RhCl(η²-CS₂)(PPh₃)(py)₂. The formation of the CS complexes occurs in two ways. Either by direct sulfur abstraction from the Rh^I(η²-CS₂) complex by PPh₃ or by a dimerisation of two CS₂ molecules and elimination of a CS moiety, resulting in a Rh^III-thiocarbonyl-trithiocarbonato complex, immediately followed by demolition of the trithiocarbonato-CS^?2₃ fragment, by PPh₃ to SPPh₃ and CS₂.Complexes containing a CS^?2₃ fragment, but no CS moiety, can also be identified by IR measurements. These products may be formed in a sidereaction upon elimination of CS.     

The formation of alkyne and alkynyl complexes by reaction of 1-alkynes with trans-[M(N2)2(PH2PCH2CH2PPh2)2] (M  Mo OR W) and with [Mo(Ph2PCH2PPh2)3]: X-ray structure of trans-[Mo(CCPh)2(PH2PCH2CH2PPh2)2]

Reaction of RCCH (R  Ph, CO₂Meor CO₂Et) with trans-[M(N₂)₂(dppe)₂] (M  Mo or W; dppe  Ph₂PCH₂CH₂PPh₂) or [Mo(dppm)₃] (dppm  Ph₂PCH₂PPh₂) gives the alkyne complexes [M(RCCH)₂(diphos)₂] (diphos  dppe, M  Mo, R = Ph; dihpos  dppm, M  Mo, R  Ph or CO₂Me) and the alkynyl complexes trans-[M(cCR)₂(dppe)₂], [MH₂(CCR)₂ (dppe)₂] (M  Mo or W. R  Ph, CO₂Me or CO₂Et) and cis-[WH(CCCO₂Me)(dppe)₂]: the X-ray structure of trans-[Mo(CCPh)₂(dppe)₂] is reported.     

Spectroscopic investigations on the structure and fluxionality of the trihaptocycloheptatrienyl complexes [MX(CO)2(LL)(η3-C7H7)] (M  Mo,W; X  I,Cl; LL  bisphosphine or diamine) and synthesis of the tetracyanoethene adducts [WI(CO)2{Ph2P(CH2)nPPh2}{η3-C9H7(CN)4}] (n = 1 or 2)

Spectroscopic investigations, including ³¹P, ¹H and ¹³C NMR studies, on the formally 6-coordinate bisphosphine complexes [MX(CO)₂{Ph₂P(CH₂)_nPPh₂}(η³-C₇H₇)] (M  Mo, W; X  I, Cl; n = 2 (dppe), n = 1 (dppm); C₇H₇  cycloheptatrienyl) reveal a structure with no molecular plane of symmetry in which inequivalent P-donor atoms are arranged cis-cis and cis-trans to the two mutually cis-carbonyl groups. The dppe complexes exhibit a fluxional process which interconverts inequivalent phosphorus environments. Low temperature ¹H and ¹³C NMR studies on the diamine derivatives [MCl(CO)₂(H₂NCH₂CH₂NH₂)(η³-R)] (M  Mo, W, R  C₇H₇; M  Mo, R  C₃H₅ (allyl)) imply that the non-symmetric structure of the bisphosphine analogues is adopted. The adducts [WI(CO)₂{Ph₂P(CH₂)_n-PPh₂} {η³-C₉H₇(CN)₄}] (n = 1 or 2) are formed by tetracyanoethene addition to the trihapto-bonded cycloheptatrienyl ring of the tungsten complexes [WI(CO)₂-{Ph₂P(CH₂)_nPPh₂}(η³-C₇H₇)] (n = 1 or 2).     

Para-hydrogen-induced polarization in rhodium complex-catalyzed hydrogenation reactions

The homogeneous hydrogenation of PhCCH catalyzed by RhClL₃, Rh(COD)L₂⁺, and Rh(COD)dppe⁺ (L  PPh₃; COD1,5-cyclooctadiene; dppe = 1,2-bis(diphenylphosphino)ethane) has been investigated using para-hydrogen-induced polarization (PHIP) which allows that in accord with earlier studies, for RHClL₃ the addition of H₂ is reversible, whereas for Rh(CO)(dppe)⁺ and Rh(COD)L₂⁺, H₂ addition in hydrogenation catalysis is irreversible.     

Reactions of 1,4-diaza-3-methylbutadien-2-ylpalladium(II) derivatives with chloro-bridged rhodium(I) complexes

The reactions of the organometallic 1,4-diazabutadienes, RN=C(R′)C(Me)=NR″ [R = R″ = p-C₆H₄OMe, R′ = trans-PdCl(PPh₃)₂ (DAB); R = p-C₆H₄OMe, R″ = Me, R′ = trans-PdCl(PPh₃)₂ (DAB^I; R = R″ = p-C₆H₄OMe, R′ = Pd(dmtc)-(PPh₃), dmtc = dimethyldithiocarbamate (DAB^II); R = R″ = p-C₆H₄OMe, R′ = PdCl(diphos), diphos = 1,2-bis(diphenylphosphino)ethane (DAB^III)] with [RhCl(COD)]₂ (COD = 1,5-cyclooctadiene, Pd/Rh ratio = $\text{1}\text{2}$) depend on the nature of the ancillary ligands at the Pd atom in group R′. In the reactions with DAB and DAB^I transfer of one PPh₃ ligand from Pd to Rh occurs yielding [RhCl(COD)(PPh₃)] and the new binuclear complexes [Rh(COD) {RN=C(R?)-C(Me)=NR″}], in which the diazabutadiene moiety acts as a chelating bidentate ligand. Exchange of ligands between the two different metallic centers also occurs in the reaction with DAB^II. In this case, the migration of the bidentate dmtc anion yields [Rh(COD)Pdmtc] and [Rh(COD) {RN=C(R?)C(Me)=NR″}]. In contrast, the reaction with DAB^III leads to the ionic product [Rh(COD)- (DAB^III)][RhCl₂(COD)], with no transfer of ligands. The cationic complex [Rh(COD)(DAB^III)]⁺ can be isolated as the perchlorate salt from the same reaction (Pd/Rh ratio = 1/1) in the presence of an excess of NaClO₄. In all the binuclear complexes the coordinated 1,5-cyclooctadiene can be readily displaced by carbon monoxide to give the corresponding dicarbonyl derivatives. The reaction of [RhCl(CO)₂]₂ with DAB and/or DAB^I yields trinuclear complexes of the type [RhCl(CO)₂]₂(DAB), in which the diazabutadiene group acts as a bridging bidentate ligand. Some reactions of the organic diazabutadiene RN=C(Me)C(Me)=NR (R = p-C₆H₄OMe) are also reported for comparison.     

Rhodium Complexes Containing O‐Bonded NHxMe2−xCHO (x=0, 1, 2): X‐Ray Structure of [Rh(PPh3)3(OCHNHMe)]ClO4

Displacement of norbornadiene (nbd; bicyclo[2.2.1]hepta‐2,5‐diene) from [Rh(PPh₃)₂(nbd)]ClO₄ by hydrogenation in the presence of PPh₃ and formamide or Me‐substituted derivatives, results in the formation of O‐bonded formamide complexes [Rh(PPh₃)₃(OCHNH_xMe_2−x)]ClO₄ (x=0, 1, 2) rather than N‐bonded derivatives. These have been characterised by spectroscopic measurements and, in the case of [Rh(PPh₃)₃(OCHNHMe)]ClO₄, by X‐ray crystallography. All undergo oxidative addition with H₂, and the rates of ligand exchange in the Rh^I and Rh^III complexes have been determined by magnetisation‐transfer measurements.     

The reaction between [Pt(cod)Cl(PMe2Ph)]BF4 and aryltrimethyltin compounds

The complex [Pt(cod)Cl(PMe₂Ph)]BF₄ reacts in dichloromethane with SnArMe₃ compounds having Ar = 2-thienyl, 2-benzol [b]thienyl, or 2-benzo[b]furyl to give air-stable cationic aryl complexes [Pt(cod)Ar(PMe₂Ph)]BF₄. No reaction takes place when Ar  Ph. The cod ligand in the new complexes can be readily replaced by ligands such as PMe₂Ph, dppe, or 4-dimethylaminopyridine. The¹H and³¹P-{¹H} NMR parameters of the various complexes are reported.     

Redox properties of the carbyne,aminocarbyne and η2-vinyl complexes trans-[ReCl(LH)(dppe)2][BF4] (LH  CCH2But,CCH2Ph,CNH2 or η2-C(CH2Ph)CH2) and of their parent vinylidene,isocyanide and allene compounds

The redox properties of the carbyne-, aminocarbyne- and η²-vinyl-(metallacyclopropene) complexes trans-[ReCl(LH)(dppe)₂][BF₄] (1; LH  CCH₂R (R Bu^t or Ph), CNH₂ and η²-C(CH₂Ph)CH₂; dppe  Ph₂PCH₂CH₂PPh₂), as well as of their parent vinylidene, isocyanide and allene complexes, trans-[ReClL(dppe)₂] (2; L  CCHR, CNH or

, have been studied by cyclic voltammetry and controlled potential electrolysis in aprotic media. The results are interpreted in terms of anodically- or cathodically-induced β-dehydrogenation processes of complexes (1), to give the corresponding compounds (2) (in the oxidized or the neutral form), as well as of a reversible dissociation of the former into the latter, in a basic solvent. The electrochemical P_L ligand parameter has been estimated for all these ligands.     

A novel reaction producing the rhodium(I) complexes with π-coordinated tetraphenylborate anion, (π-PhBPh3). X-ray study of [Rh(PPh3)2(π-PhBPh3)]

Treating the complexes [Rh(TFA)(PPh₃)₂], [Rh(HFA)(PPh₃)₂], and [Rh(TFA)(Cod)] (TFA - trifluoroacetylacetonate, HFA - hexafluoroacetylacetonate, Cod - 1,5 cyclooctadiene) with an excess of NaBPh₄ in acetonitrile yields the rhodium(I) complexes with coordinated [BPh₄]⁻ anion, [Rh(PPh₃)₂(π-PhBPh₃)] · 2MeCN (I) and [Rh(Cod)(π-PhBPh₃)] (II). The reactions present a new example of β-diketonate ligand replacement. The ¹H, ³¹P, and ¹¹B NMR spectra of I and II are discussed. [Rh(PPh₃)₂(π-PhBPh₃)] has been characterized by single crystal X-ray analysis.     

Rhodium(I) indazole and indazolate complexes

The preparation of cationic indazole (HIdz) rhodium(I) complexes of the types [(diolefin)Rh(HIdz)₂]ClO₄ and [(CO)₂Rh(HIdz)₂]ClO₄ is described. Neutral binuclear rhodium(I) complexes of the type [Y₂Rh(μ-Idz)]₂ (Y₂  COD, TFB, NBD, (CO)₂ or (CO)(PPh₃)) are obtained by treating the corresponding complexes [Y₂RhCl]₂ with indazole and organic or inorganic bases. The cationic mononuclear derivatives react with the solvated species [Y₂Rh(acetone)_x]ClO₄ in the presence of triethylamine to give neutral binuclear complexes of the types [(CO)₂Rh(μ-Idz)₂Rh(diolefin)], [(Ph₃P)(CO)Rh(μ-Idz)₂Rh(diolefin)] and [(diolefin)Rh(μ-Idz)Rh(diolefin′)] (diolefin  COD, TFB or NBD; diolefin′  COD or TFB). Alternative methods for the synthesis of the binuclear complexes are also described.     

Carbonyl rhodium(I) complexes with α-diimines ligands

The reactions of [Rh(CO)₂Cl]₂ with α-diimines, RN=CR′-CR′=NR (R = c-Hex, C₆H₅, p-C₆H₄OH, p-C₆H₄CH₃, p-C₆H₄OCH₃, R′ = H; R = c-Hex, C₆H₅, p-C₆H₄OH, p-C₆H₄OCH₃; R′ = Me) in 2:1 Rh/R-dim ratio gave rise to ionic compounds [(CO)₂Rh.R-dim(R′,R′)][Rh(CO)₂Cl₂] which have been characterized by elemental analyses, electrical conductivity, ¹H-NMR and electronic and IR spectroscopy. Some of these complexes must involve some kind of metal-metal interaction. The complex [Rh(CO)₂Cl.c-Hex-dim(H,H)] has been obtained by reaction of [Rh(CO)₂Cl]₂ with the c-Hex-dim(H,H) ligand in 1:1 Rh/R-dim ratio. The reactions between [(CO)₂Rh.R-dim(H,H)][Rh(CO)₂Cl₂](R = c-Hex or p-C₆H₄OCH₃) with the dppe ligand have been studied. The known complex RhCl(CO)(PPh₃)₂ has been isolated from the reaction of [(CO)₂Rh.R-dim(H,H)]-[Rh(CO)₂Cl₂] (R = c-Hex or p-C₆H₄OCH₃) with PPh₃ ligand.     

The cis-Re(Ph2PCH2CH2PPh2)2)+ metal centre. Synthesis and molecular structure of the dinitrile complex cis-[Re(NCC6H4Me-4 2(Ph 2 PCH 2 CH 2 PPh 2 2 ][BF4]

Reaction of NCC₆H₄X-4 (X  Me, OMe, or Cl) with trans-[ReCl(N₂)(dppe)₂] (dppe  Ph₂PCH₂CH₂PPh₂), at room temperature, in the presence of Tl[BF₄], gives the corresponding complexes cis-[Re(NCC₆H₄X-4)₂(dppe)₂][BF₄] (1); the crystal structure of 1 (X  Me) has been determined by single crystal X-ray diffraction analysis.     

Hydrogen abstraction and dimerisation reactions of some organo-transition metal free radicals

The 17-electron species [M(CO)_5χL_χ] (M  Mn, Re, χ  0; M  Mn, Re; L  Ph₃P, χ  1, 2; M  Mn, Re; L  (o-MeC₆H₄O)₃P, χ  2; M  Mn; L  (p-ClC₆H₄O)₃P, (PhO)₃P, χ  2; M  Mn; L  P(OMe)₃, χ  3) have been generated by one electron oxidation of the corresponding anions and show typical radical reactivity, undergoing dimerisation or hydride abstraction in reactions controlled by steric effects. Evidence is presented for the source of the hydrogen atom. The 19-electron species [M(CO)₃(η⁷-C₇H₇)]^? (M  Cr, Mo) and [Fe(CO)₃(η⁵-C₆H₇)]^?, generated by reduction of the corresponding cations, undergo dimerisation at the organic ligand. Similar treatment of [Fe(CO)₂-L(η-cp)]⁺ (L  CO, PPh₃, P(OPh)₃, Me₂CO) yields [Fe₂(CO)₄(η-cp)₂] and these reduction reactions are rationalised in terms of the nature of the HOMO in the intermediate radical. Similar reduction of [Rh(diphos)₂]⁺ yield the 17-electron intermediate [Rh(diphos)₂] and this also undergoes hydrogen abstraction.     

Imidazolate bridged polynuclear rhodium(I) complexes. X-ray structure of [Rh(2-Meimidazolate)(CO)2]4

The synthesis and properties of polynuclear complexes of general formulae [M(RIm)(diolefin)_x, [M(RIm)(CO)₂]_x and [M(RIm)(CO)L]_x (M  Rh, Ir; RIm  imidazolate, 2-methylimidazolate, 2-benzylbenzimidazolate; L  PPh₃ or P(OPh)₃) are reported. The crystal structure of the novel complex [Rh(2-MeIm)-(CO)₂]₄ (2-MeIm  2-methylimidazolate) has been determined by X-ray methods. The crystals are orthorhombic, space group P2₁2₁2₁, with Z  4 in a unit cell of dimensions a 19.427(12), b 13.419(8), c 12.346(9) Å. The structure has been solved by combined Patterson and direct methods and refined by full-matrix least-squares to R  0.043 for 937 independent observed reflections. It consists of discrete tetrameric complexes in which each Rh atom is in a nearly cis square planar arrangement, bonded to two carbon atoms of carbonyl groups and to two nitrogen atoms of two 2-methylimidazolate ligands, each of which, acting as an exo-bidentate ligand, bridging two metal atoms, so that the four bridging 2-MeIm ligands and the four Rh atoms form a multiatomic ring.     

Platinum(II), palladium(II), nickel(II), and gold(I) complexes of the “electrospray-friendly” thiolate ligands 4-SC5H4N− and 4-SC6H4OMe−

The series of platinum(II), palladium(II), and nickel(II) complexes [ML₂(dppe)] [M = Ni, Pd, Pt; L = 4–SC₅H₄N or 4–SC₆H₄OMe; dppe = Ph₂PCH₂CH₂PPh₂] containing pyridine-4-thiolate or 4-methoxybenzenethiolate ligands, together with the corresponding gold(I) complexes [AuL(PPh₃)], were prepared and their electrospray ionization mass spectrometric behavior compared with that of the thiophenolate complexes [M(SPh)₂(dppe)] (M = Ni, Pd, Pt) and [Au(SPh)(PPh₃)]. While the pyridine-4-thiolate complexes yielded protonated ions of the type [M + H]⁺ and [M + 2H]²⁺ ions in the Ni, Pd, and Pt complexes, an [M + H]⁺ ion was only observed for the platinum derivative of 4-methoxybenzenethiolate. Other ions, which dominated the spectra of the thiophenolate complexes, were formed by thiolate loss and aggregate formation. The X-ray crystal structure of [Pt(SC₆H₄OMe–4)₂(dppe)] is also reported.     

ESR investigation of the substitution reactions in rhodium(I) complexes with spin-labeled ligands

A number of new spin-labelled Rh^I complexes containing both the 3,6-ditert-butyl-o-benzosemiquinone (3,6-SQ) fragment and n- and π-donor ligands have been prepared. The tetracoordinate derivatives of the composition L₂Rh-(3,6-SQ), where L  CO, P(OPh)₃, L  1/2 1,5-COD and the pentacoordinate complex (PPh₃)₂Rh(3,6-SQ)(CO) were isolated in individual state, the formation of other rhodium compounds was registered by ESR spectroscopy. The presence of an o-benzosemiquinolate ligand in the molecule with the unpaired electron located essentially on this fragment does not significantly influence on the reactivity of the metal ion in most cases; the n- and π-donor ligands exchange reactions studied by ESR confirm this fact. (PPh₃)₂Rh(3,6-SQ) has an abnormal distribution of spin density of the unpaired electron in the molecule, mostly located on the metal atom, this derivative bearing a close analogy to the rhodium(II) (d⁷) complexes.     

The electronic properties of isocyanides at rhenium—dinitrogen binding sites. Preparation and redox properties of the isocyanide complexes trans-[ReCl(CNR)(Ph2PCH2CH2PPh2)2]

The isocyanide complexes trans-[ReCl(CNR)(dppe)₂] (R  Me, Bu^t, C₆H₄CH₃-4, C₆H₄CH₃-2, C₆H₄Cl-4, C₆H₄OCH₃-4 and C₆H₃Cl₂-2,6; dppe  Ph₂PCH₂CH₂PPh₂) have been prepared by isocyanide displacement of dinitrogen from the parent complex trans-[ReCl(N₂)(ddpe)₂]. Their redox properties have been studied by cyclic voltammetry and are interpreted on the basis of the electronic properties and the geometry of the ligating isocyanides which are believed to be bent in these complexes, appearing to exhibit ligand parameter (P_L) values ca. +0.3 V higher than those which would be expected for linear geometry. A very high polarisability (B ? 3.4) is observed for the {ReCl(dppe)₂} site.     

Rhodium Complexes in P−H Bond Activation Reactions

The feasibility of oxidative addition of the P−H bond of PHPh₂ to a series of rhodium complexes to give mononuclear hydrido-phosphanido complexes has been analyzed. Three main scenarios have been found depending on the nature of the L ligand added to [Rh(Tp)(C₂H₄)(PHPh₂)] (Tp= hydridotris(pyrazolyl)borate): i) clean and quantitative reactions to terminal hydrido-phosphanido complexes [RhTp(H)(PPh₂)(L)] (L=PMe₃, PMe₂Ph and PHPh₂), ii) equilibria between Rh^I and Rh^III species: [RhTp(H)(PPh₂)(L)]⇄[RhTp(PHPh₂)(L)] (L=PMePh₂, PPh₃) and iii) a simple ethylene replacement to give the rhodium(I) complexes [Rh(κ²-Tp)(L)(PHPh₂)] (L=NHCs-type ligands). The position of the P−H oxidative addition–reductive elimination equilibrium is mainly determined by sterics influencing the entropy contribution of the reaction. When ethylene was used as a ligand, the unique rhodaphosphacyclobutane complex [Rh(Tp)(η¹-Et)(κ^C,P-CH₂CH₂PPh₂)] was obtained. DFT calculations revealed that the reaction proceeds through the rate limiting oxidative addition of the P−H bond, followed by a low-barrier sequence of reaction steps involving ethylene insertion into the Rh−H and Rh−P bonds. In addition, oxidative addition of the P−H bond in OPHPh₂ to [Rh(Tp)(C₂H₄)(PHPh₂)] gave the related hydride complex [RhTp(H)(PHPh₂)(POPh₂)], but ethyl complexes resulted from hydride insertion into the Rh−ethylene bond in the reaction with [Rh(Tp)(C₂H₄)₂].