80737-40-2Relevant academic research and scientific papers
Metal-formaldehyde chemistry: Metal-promoted elementary transformations of formaldehyde
Gambarotta, Sandro,Floriani, Carlo,Chiesi-Villa, Angiola,Guastini, Carlo
, p. 2425 - 2433 (2008/10/08)
Paraformaldehyde reacts with vanadocene, cp2V (I; cp = η5-C5H5), in a toluene solution to form [cp2V(η2-CH2O)] (II). The bonding mode of formaldehyde was determined by an X-ray analysis [V-C = 2.092 (8) A?, V-O = 1.955 (5) A?, and C-O = 1.353 (10) A?]. The formation of II occurred with simultaneous generation of a significant amount of HCOOMe, as a consequence of the fact that II can react further with paraformaldehyde to form HCOOMe. Disproportionation of CH2O to HCOOMe was observed when the CH2O ligand was removed from II by using carbon monoxide. Oxymethylene ligands containing a vanadium-carbon σ bond have been formed by reacting complex II with Lewis acids and alkylating agents. Lewis acids, like BF3 or TiCl4, or alkylating agents, such as Et3OBF4 or MeSO3F, gave very unstable oxymethylene compounds which underwent homolytic fission of one V-C σ bond. Stable oxymethylene compounds were isolated when the alkylation of II was carried out by using acyl halides MeCOCl and PhCOCl. Compounds isolated in crystalline forms were [cp2V(Cl)(OC(O)Me)] (VI; v(CO) = 1710 cm-1) and [cp2V(Cl)(OC(O)OPh)] (VII; v(CO) = 1690 cm-1). The ionization of the V-Cl bond in VI and VII allowed the second oxygen to bind vanadium forming metallacycles [cp2V(CH2-O-C(O)-Me)](BPh4) (VIII) and [cp2V(CH2-O-C(O)-Ph)](BPh4) (IX). The CO stretching band is significantly lowered, to 1605 cm-1 in VIII and to 1600 cm-1 in IX. An important lengthening of the V-C and C-O bond distances accompanying the acylation of formaldehyde [V-C = 2.159 (4) A? and C-O = 1.474 (5) A? in complex VIII; V-C = 2.170 (7) A?, and C-O = 1.481 (8) A? in complex IX] was observed. Complexes VIII and IX did not react or only slightly reacted with CO, inducing homolytic cleavage of the V-C bond and forming [cp2V(CO)2]+. Nickel(0)-phosphine complexes [Ni(PR3)4] (R = n-Bu, XV; R = Ph, XVI) and [Ni(PPh3)2(C2H4)] (XVII) promoted decomposition of formaldehyde to CO and H2, and they formed [Ni(PR3)3(CO)] (XVIII and XIX) and [Ni(PPh3)2(CO)2] (XX), respectively. Reaction of these complexes was stoichiometric, but for XVII the reaction was slightly catalytic when carried out in vacuo. A titanium(III) complex, [cpTi(Cl)2(THF)1.5] (XXI), was able to promote the deoxygenation of formaldehyde to ethylene, while titanium is converted into different oxo complexes, namely, [cpTi(Cl)2]2(μ-O) (XXII) and [cpTi(Cl)(μ-O)]4 (XXIII). Suggestions are given on the organometallic precursors leading to the deoxygenation of formaldehyde. Crystallographic details for complex II: space group C2/c (monoclinic); a = 13.634 (3) A?, b = 6.812 (1) A?, c = 20.528 (4) A?, β = 103.24 (2); V = 1855.9 (6) A?3; Z = 8; Dcalcd = 1.51 g cm-3. The final R factor was 0.050 (Rw = 0.051) for 820 observed reflections. Crystallographic details for complex VIII: space group P1 (triclinic); a = 14.542 (4) A?, b = 11.108 (4) A?, c = 10.019 (3) A?, α = 103.51 (3)°, β = 90.59 (3)°, γ = 110.39 (3)°; V = 1467.5 (9) A?3; Z = 2; Dcalcd = 1.30 g cm-3. The final R factor was 0.057 (Rw = 0.064) for 2949 observed reflections. Crystallographic details for complex IX: space group Cc (monoclinic); a = 11.233 (1) A?, b = 16.748 (1) A?, c = 17.475 (1) A?, β = 95.57 (1)°; V = 3272.1 (4) A?3; Z = 4; Dcalcd = 1.29 g cm-3. The final R factor was 0.037 (Rw = 0.039) for 1789 observed reflections.
