Fernando Villafañe

Structure and Dynamic Behavior of (η3‐Allyl)bromodicarbonylmolybdenum(II) Complexes Containing Polydentate 2‐Pyridylphosphanes or Their Oxides as Chelating Ligands: Occurrence of Three Fluxional Processes

The pseudo-octahedral complexes [Mo(η3-allyl)Br(CO)2(PPynPh3–n-P,N)] (Py = 2-pyridyl; n = 2, 3) and [Mo(η3-allyl)Br(CO)2(OPPymPh3–m-O,N)] (m = 1, 2, 3) undergo three different dynamic processes in solution, depending on the chelating ligand. The complexes containing PPhPy2 and PPy3 as chelating P,N-donors undergo a novel “pivoted double switch” mechanism which scrambles two equatorial coordination sites with racemization, while maintaining the identity of the phosphorus atom trans to the allyl ligand. The complexes containing 2-pyridylphosphane oxides as chelating O,N-donors undergo a nondissociative intramolecular trigonal-twist (or turnstile) rearrangement which maintains the identity of the phosphane oxide oxygen atom coordinated in an equatorial position. All the complexes containing uncoordinated pyridyls undergo a slow dissociative exchange of pyridyls without coordination site scrambling. The structure of the complex [Mo(η3-allyl)Br(CO)2(OPPy3-O,N)] has been determined by X-ray diffraction.

Enantiomerically enriched ‘carbanions’:: Studies on the stereochemical course of selective transformations of metal alkyls

Abstract Two (aminomethyl)(lithiomethyl)silanes Ph 2 Si(CH 2 Li)(CH 2 NC 5 H 10 ) (NC 5 H 10 =1-piperidinyl) ( 2 ) and Me 2 Si{[ R ]-[CHLiPh]}(CH 2 SMP) {SMP=1-[( S )-2-(methoxymethyl)pyrrolidinyl]} [( R , S )- 17 ] are presented including their solid state structures, the first one non-chiral, the latter highly diastereomerically enriched. By metathesis reactions with metal(II) halides (metal=Mg, Ga, Pd, Cd and Hg), the corresponding bis{[(aminomethyl)silyl]methyl}metal(II) compounds or the [(aminomethyl)silyl]methylmetal(II) halides were obtained. In the case of highly diastereomerically enriched (aminomethyl)(lithiomethyl)silane ( R , S )- 17 , the ‘carbanionic’ fragment could be transferred with high stereoselectivities on the metals Hg and Pd. For all of the compounds, the solid state molecular structures were determined.

Phenylbis(2- pyridyl)phosphine: P- vs. N,N′-coordination in carbonylmolybdenum-(O) and -(II) complexes

The first carbonyl molybdenum-(O) and -(II) complexes with phenylbis(2-pyridyl)phosphine (PPhpy2) have been synthesized. PPhpy2 reacts with [Mo(CO)5(NCMe)] to give [Mo(CO)5(PPhpy2-P)]. With [Mo(CO)4(NBD)] (NBD = norbornadiene) it gives [Mo(CO)4(PPhpy2-P)2] when a 2 : 1 ratio is used, or [MO(CO)4(py2PhPN,N′)] for a 1 : 1 ratio. Decarbonylation of any of these pyridylphosphine complexes leads to an oligomer of formula {MO(CO)3(μ-PPhpy2)}n, which is also obtained after heating [MO(CO)6] in solution with an equimolar amount of PPhpy2. The oligomer undergoes oxidative addition by iodine or allylbromide to give [MoI2(CO)3(py2PhPN,N′)], or [MoBr(η3-CH2CHCH2)(CO)2(py2PhPN,N′)], respectively. These complexes are also obtained by addition of equimolar amounts of PPhpy2 to solutions of [MoI2(CO)3(NCMe)2] and MoBr(η3-CH2CH CH2)(CO)2(NCMe)2, respectively. The ligand tends to act as a P-donor towards molybdenum(O) substrates, and as a chelating N,N′-donor in molybdenum (II) complexes.

Synthesis of mer-tricarbonyls of manganese(I) with N-donor chelate ligands

Abstract The first mer -tricarbonyl complexes of manganese(I) with N -donor chelate ligands, namely mer -[Mn(CO) 3 (CNR)(NN)]ClO 4 , where CNR = CNBu t , NN = 1,10-phenantroline (phen) or 2,2′-bipyridine (bipy), have been obtained from the reactions of fac -[Mn(CO) 3 (Me 2 CO)(NN)]ClO 4 with isocyanides, CNR. Other members of the [Mn(CO) 4- n (CNR) n (NN)]ClO 4 ( n = 1,2,3,4) series have also been synthesized: viz., fac -[Mn(CO) 3 (CNR)(NN)]ClO 4 (Ia-d) and cis,cis -[Mn(CO) 2 (CNR) 2 (NN)]ClO 4 (CNR = CNBu t , CNPh) (IIa-d), cis,cis -)[Mn(CO) 2 (CNR)(CNR′)(NN)]ClO 4 (CNR = CNPh, CNR′ = CNBu t and CNR = CNBu t , CNR′ = CNPh) (IIe-f), fac -[Mn(CO)(CNBu t ) 3 (NN)]ClO 4 , (IVa-b), and [Mn(CNPh) 4 (NN)]ClO 4 ; (NN) represents phen or bipy. (See Scheme 1 and Table 1).

Self‐Assembly of Pyramidal Tetrapalladium Complexes with a Halide at the Apex

Halide ions act as the template for the self-assembly of tetrapalladium macrocyclic pyramidal structures. These undergo easy inversion in which the halide ion apparently jumps across the macrocycle.

The first pyrazole molybdenum(0) complexes: cis-[Mo(CO)4(Hdmpz)2] crystallizes as a NH⋯OC hydrogen-bonded dimer

Abstract The reactions of [Mo(CO)4(NBD)] with two equivalents of Hpz (pyrazole) or Hdmpz (3,5-dimethylpyrazole) in hexane lead to the precipitation of cis-[Mo(CO)4(Hpz)2] or cis-[Mo(CO)4(Hdmpz)2], which are the first pyrazole complexes of molybdenum(0). In the solid state structure of cis-[Mo(CO)4(Hdmpz)2], two molecules are self-assembled by intermolecular hydrogen bonds between the N-bound hydrogen of one Hdmpz ligand and a oxygen atom of a carbonyl group. This explains the lack of planarity observed for the nitrogen donor atom of the Hdmpz involved in the intermolecular interaction. The complexes are unstable in solution and as solids.

[Pd(Fmes)I{NMe2(CH2-o-C6H4-I)-N, I}], a palladium(II) complex with I- and organic iodide as trans ligands

The treatment of [Pd(dmba)(Fmes)(OH2)] with I2 leads to the formation of [Pd(Fmes)I{NMe2(CH2-o-C6H4-I)-N,I}]. The X-ray structure shows that a new halocarbon ligand, (2-iodobenzyl)dimethylamine has been formed and is acting as N–I chelate. The two different types of iodine, one iodide ligand and one organic iodide coordinated to Pd, are mutually trans and display essentially identical Pd–I distances.

Synthesis, crystal structure and heterometallic derivatives of [Mo2Cp2(μ-σ,π-CNtBu)(PPh2CH2PPh2-P)(CO)3] (tBu = C(CH3)3, Cp = η-C5H5)

Abstract The dppm ligand (Ph 2 PCH 2 PPh 2 ) in [Mo 2 Cp 2 (CO) 4 (μ-dppm)] (Cp = η-C 5 H 5 ) undergoes ring-opening upon reaction with NCMe or CN t Bu ( t Bu = C(CH 3 ) 3 ), to give [MoCp(CO)(NCMe)(dppm)][MoCp(CO) 3 ] or [Mo 2 Cp 2 (μ-σ,π-CN t Bu)(dppm-P)(CO) 3 ], respectively. The crystal structure of the latter complex is described as well as its reactions with sources of the metal fragments ML n [ML n : Fe(CO) 4 , Mo(CO) 5 , MnBr(CO) 4 , CuCl] to give the heterometallic species [ML n (μ-dppm)MoCp(CO)(μ-σ,π-CN t Bu)MoCp(CO) 2 ].

Molybdenum – and tungsten(II) monometallic 3-(2-pyridyl)pyrazole and bimetallic 3-(2-pyridyl)pyrazolate complexes

Molybdenum and tungsten complexes containing the pypzH (3-(2-pyridyl)pyrazole) ligand as a chelating bidentate are prepared: [Mo(CO)(4)(pypzH)], cis-[MoBr(η(3)-allyl)(CO)(2)(pypzH)], cis-[MoCl(η(3)-methallyl)(CO)(2)(pypzH)], [MI(2)(CO)(3)(pypzH)] (M = Mo, W) from [Mo(CO)(4)(NBD)] or the adequate bis(acetonitrile) complexes. The deprotonation of the molybdenum allyl or methallyl complexes affords the bimetallic complexes [cis-{Mo(η(3)-allyl)(CO)(2)(μ(2)-pypz)}](2) or [cis-{Mo(η(3)-methallyl)(CO)(2)(μ(2)-pypz)}](2) (μ(2)-pypz = μ(2)-3-(2-pyridyl-κ(1)N)pyrazolate-2κ(1)N). The allyl complex was subjected to an electrochemical study, which shows a marked connection between both metallic centres through the bridging pyridylpyrazolates.

Coordination versus coupling of dicyanamide in molybdenum and manganese pyrazole complexes.

The reactions of cis-[MoCl(η(3)-methallyl)(CO)(2)(NCMe)(2)] (methallyl = CH(2)C(CH(3))CH(2)) with Na(NCNCN) and pz*H (pzH, pyrazole, or dmpzH, 3,5-dimethylpyrazole) lead to cis-[Mo(η(3)-methallyl)(CO)(2)(pz*H)(μ-NCNCN-κ(2)N,N)](2) (pzH, 1a; dmpzH, 1b), where dicyanamide is coordinated as bridging ligand. Similar reactions with fac-[MnBr(CO)(3)(NCMe)(2)] lead to the pyrazolylamidino complexes fac-[Mn(pz*H)(CO)(3)(NH═C(pz*)NCN-κ(2)N,N)] (pzH, 2a; dmpzH, 2b), resulting from the coupling of pyrazol with one of the CN bonds of dicyanamide. The second CN bond of dicyanamide in 2a undergoes a second coupling with pyrazole after addition of 1 equiv of fac-[MnBr(CO)(3)(pzH)(2)], yielding the dinuclear doubly coupled complex [{fac-Mn(pzH)(CO)(3)}(2)(μ-NH═C(pz)NC(pz)=NH-κ(4)N,N,N,N)]Br (3). The crystal structure of 3 reveals the presence of two isomers, cis or trans, depending on whether the terminal pyrazoles are coordinated at the same or at different sides of the approximate plane defined by the bridging bis-amidine ligand. Only the cis isomer is detected in the crystal structure of the perchlorate salt of the same bimetallic cation (4), obtained by metathesis with AgClO(4). All the N-bound hydrogen atoms of the cations in 3 or 4 are involved in hydrogen bonds. Some of the C-N bonds of the pyrazolylamidino ligand have a character intermediate between single and double, and theoretical studies were carried out on 2a and 3 to confirm its electronic origin and discard packing effects. Calculations also show the essential role of bromide in the planarity of the tetradentate ligand in the bimetallic complex 3.