Mirto Mozzon

Reactions of transition metal-coordinated nitriles

Abstract The reaction chemistry of nitriles, RCN, where R is usually an organyl group, with transition metal complexes is reviewed. The review surveys data published during the period 1977-early 1994 on new reaction processes such as insertion into metal-hydrogen and -carbon bonds, coupling between one nitrile and an unsaturated metal fragment or between two nitriles, reduction to amines, attack by protic and aprotic nucleophiles and electrophilic attack as well as some catalytic transformations, which result from the ability of nitriles to coordinate to transition metal centres with a consequent change in the electrophilicity or nucleophilicity of the coordinated ligand.

Platinum—alkynyl and —alkyne complexes: old systems with new chemical and physical perspectives

Abstract The chemistry of alkynyl and alkyne ligands in platinum complexes of different oxidation states is described. The review focuses on the synthetic aspects of mono- and polynuclear compounds and on the reactivity of σ-alkynyl and π-alkyne species in different stoichiometric reactions such as insertion, addition of nucleophiles and electrophiles, rearrangements and isomerization processes and also some catalytic additions of heteroatoms (B, Si, S) across the CC triple bond. The relevant features of polynuclear complexes bearing the CC group in dendrimers and organometallic polymers are briefly reported.

Synthesis and spectroscopic investigation of cis and trans isomers of bis(nitrile)dichloroplatinum(II) complexes

Abstract A series of bis(nitrile) complexes cis- and trans-Cl2Pt(NCR)2(R=C6H5,p-CH3C6H4, p-CF3C6H4, o-CH3C6H4,CH3, CH3CH2, CH3CH2CH2, (CH3)2CH, (CH3)3C) has been prepared by either one of the two methods, K2PtCl4/H2O/ RCN(excess) or PtCl2/RCN(neat), both of which usually yield the nitrile complexes as a mixture of cis and trans isomers in different ratios depending on the experimental conditions such as the reaction temperature and the reaction time. The separation of the stereoisomers of each bis(nitrile) compound could be achieved by fractional crystallization by taking advantage of the generally higher solubility of the trans species in non-polar solvents. The complexes were characterized by IR, 1H and 13C NMR spectroscopies. Some general trends of v(CN) and v(PtCl) stretching frequencies as well as of the 2J(PtC) values have been found to be useful in determining the stereogeometry of the cis and trans isomers of the Cl2Pt(NCR)2 complexes.

Functionalized ylides: new trends in organometallic chemistry

The coordination and organometallic chemistry of P- and As-carbonyl stabilized ylides is reviewed. As a general feature, the coordination chemistry of R3ECHCOR′-type (E=P, As) ligands appears to be dominated by C(ylide) metal coordination, although a few examples of O(ylide)-bound complexes are known. The factors addressing C(ylide)-vs. O(ylide)-coordination in Pt(II) and Pd(II) systems are examined. The Ni(II) complexes containing P,O-chelate ylide ligands are also discussed, with a special emphasis on their catalytic activity. The synthesis and reactivity of phosphonium functionalized isocyanides and their corresponding ylides, which provide a new route to metal coordinated indole systems, are described. Finally, the reactivity of Ph3PCCO towards metal substrates is summarized including the formation of ketenyl complexes.

Synthesis, chemical and electrochemical deprotonation reactions of aminocarbene complexes of palladium(II) and platinum(II). X-ray structure of {(PPh3)ClPt[μC,N]}2

Abstract The diaminocarbene complexes cis-Cl2(PPh3)Pt[ CN(Bu t )CH 2 CH 2 N H] (1) and cis-Cl2Pt[ CN(C 6 H 4 -p-OMe)CH 2 CH 2 N H]2 (2) have been prepared by reaction of the corresponding isocyanide derivatives with aziridine/ClCH2CH2NH3+Cl− and aziridine alone, respectively. The aminooxycarbene complex cis-Cl2Pt[ CN(C 6 H 4 -p-OMe)CH 2 CH 2 O ]2 (3) has been prepared by reaction of the bis-isocyanide derivative with 2-chloroethanol/n-BuLi. The dimeric complexes {(PPh3)BrPd[μ- CN(Me)CH 2 CH 2 N C,N]}2 (4), {(PPh3)ClPd[μ- CN (C6H4-p-OMe)CH2CH2NC,N]}2 (5), {(PPh3)ClPt[μ- CN(C 6 H 4 -p-OMe)CH 2 CH 2 N C,N]}2 (6) have been prepared by deprotonation reaction of the NH group of the corresponding mononuclear derivatives with n-BuLi. The X-ray structure of {(PPh3)ClPt[μ- COCH 2 CH 2 N C,N]}2 (7) is reported. The structural model was refined to R=0.055 (Rw=0.061) for 7442 independent reflections. Crystal data: triclinic, space group P , a=19.564(3), b=16.497(3), c=13.243(2) A, α=88.93(3), β=97.88(3), γ=91.97(3)° Z=4. The crystal contains two crystallographically independent dimer units and a disordered dichloroethane molecule. Each dimer is formed by two bridging carbene ligands which are coordinated to one platinum on one side via a PtN bond and to the second platinum via a PtC bond. The coordination geometry around each platinum atom is an irregular square with deviations in the tetrahedral direction of the bonded atoms. The anodic behaviour of these and related monocarbene, dicarbene or dinuclear dicarbene complexes has been studied by cyclic voltammetry and controlled potential electrolysis in aprotic media and shown to present irreversible oxidation waves commonly with a multi-electron character (up to four electrons) and involving liberation of protons (in a number similar to that of the transfered electrons) conceivably resulting from anodically induced NH or CH bond cleavage, the former at an amino group and the latter occurring at methylene groups activated by adjacent amino- or oxy-carbene moieties.

Influence of ancillary ligands in the coordination mode of P and As carbonyl stabilized ylides on Pt(II) systems. X-ray structure of trans-[Pt(PPh3)2(CF3) {OC(OCH3)C(H) (PPh3)}] [BF4]·0.5CH2Cl2

Abstract The carbonyl stabilized P and As Ph3PHCOR (RCH3, Ph, OCH3) and Ph3ASCHCOR (RCH3, PH, OCH3) have been reacted with some platinum(II) complexes bearing ancillary ligands with different steric hindrance, in order to determine the factors that influence the C- versus O-coordination mode of the ylides. Thus, the reactions of [(dppe)PtCl2] and [(dppv)PtCl2] with Ph3PCHCOR (R^z.dbnd;CH3, Ph) give the O-coordinated complexes, while with Ph3PCHCOOCH3 they give the corresponding C-coordinated derivatives. The reactions of trans-[PPh3)2(CF3)Pt(solv)]+BF−4 yieldd the O-coordinated compounds and the reactions with [Pt(C3H5)Cl]4 give selectivity the C-coordinated derivatives as well as the reactions with the dimer [ PlCl(P(Bu 2 ) 2 C(Me) 2 C H 2 }] 2 . The derivative trans-[Pt(PPh3)2(CF3){OC(OCH3)=C(H)(PPh3)}][BF4]] crystallizes in the triclinic group P1 (No. 2), a = 10.385(4), b = 14.844(5), c = 18.511(6) →A , α = 96.46(2), β=99.79(2), γ = 97.00(2)°, V = 2765(1) a A 3 , Z = 2 . The values of coordination distances and of the PtOC angle appear influenced by steric factors.

Syntheses and properties of cyanamide and cyanoguanidine complexes of platinum(II). X-Ray structure of trans-[Pt(CF3)(NCNEt2)(PPh3)2][BF4]

Complexes trans-[PtX(L)(PPh3)2]A [1: X = CF3; A = BF4; L = NCNH2, NCNMe2, NCNEt2, or NCNC(NH2)2. 2: X = Cl; A = BPh4; L = NCNMe2 or NCNEt2] and cis-[PtCl(L)(PPh3)2][BPh4] [3: L = NCNH2 or NCNC(NH2)2], which appear to be the first cyanamide or cyanoguanidine complexes of platinum to be reported, have been prepared by treatment of trans-[PtBr(CF3)(PPh3)2] (in CH2Cl2/acetone and in the presence of Ag[BF4]) or of cis-[PtCl2(PPh3)2] (in THF and in the presence of Na[BPh4]), respectively, with the appropriate substrate. In KBr pellets or in solution 1 (L = NCNMe2 or NCNEt2) undergoes ready replacement of the organocyanamide (under the trans influence of CF3) by bromide to regenerate trans-(PtBr(CF3)(PPh3)2]. The X-ray structure of 1 (X = CF3, A = BF4, L = NCNEt2) is also reported, and shows the presence of two apical intramolecular contacts of the metal with two ortho-hydrogen atoms of the phosphines, whereas the amine N atom of the diethylcyanamide is trigonal planar in the linear NCN framework with a delocalized π system.

Cis addition of dimethylamine to the coordinated nitriles of cis- and trans-[PtCl2(NCMe)2]. X-ray structure of the amidine complex cis-[PtCl2{E-N(H)C(NMe2)Me}2]·CH2Cl2

Abstract The reaction of cis-[PtCl2(NCMe)2] with a 5-fold excess of Me2NH in CH2Cl2 at −10°C affords in high yield the bis-amidine complex cis-[PtCl2{E-N(H)C(NMe2)Me}2] (E,E-2), where both the amidine ligands assume the E configuration. E,E-2 was characterized by X-ray structure analysis, NMR spectroscopy and electrospray ionization mass spectrometry (ESI-MS). The corresponding reactions of trans-[PtCl2(NCMe)2] with Me2NH gave the bis-amidine complex trans-[PtCl2{E-N(H)C(NMe2)Me}2] (E,E-3) and the mono-amidine derivative trans-[PtCl2{E-N(H)C(NMe2)Me}(NCMe)] (E-4).

Reactions of platinum(II)–nitrile complexes with amines. Synthesis, characterization and X-ray structure of the platinum(II)–amidine complex trans-[PtCl2{Z-N(H)C(NHMe)Me}2]

Abstract The reaction of trans -[PtCl 2 (NCMe) 2 ] with a 5-fold excess of MeNH 2 in CH 2 Cl 2 at −10°C affords in high yield the bis-amidine complex trans -[PtCl 2 { Z -N(H)C(NHMe)Me} 2 ] ( 1 ), where both the amidine ligands assume the Z configuration corresponding to the trans addition of the amine along the CN triple bond. Compound 1 has been fully characterized by spectroscopic techniques and also by X-ray diffraction analysis.

Bifunctional activation of cyanoguanidine. Synthesis and molecular structure of the azametallacycle cis-[(PPh3)2Pt{NHC(OMe)=NC(NH2)=NH}][BPh4]

Abstract The cyanoguanidine complex cis-[Pt(NCNC(NH2)2)2(PPh3)2][BPh4]2, prepared by reacting cis-[PtCl2(PPh3)2] with cyanoguanidine in the presence of Na[BPh4], readily reacts with methanol to give cis-[(PPh3)2PtNHC(OMe) = NC(NH2) = NH)] [BPh4] containing a novel type of azametallcycle whose molecuar structure is established by X-ray crystallography. Its formation involves metal-promoted nucleophilic addition of the alcohol to the cyano group of a cyanoguanidine ligand, combined with deprotonation of the guanidine unit which then chelates the Pt(II) centre.