Synthesis of Mesityl Oxide π-Complexes with Metals of Chromium Subgroup and with Iron. Theoretical and Experimental Investigation of the Ligand Dissociation Energy

Abstract

At the use of photochemical and thermochemical activation new p-complexes of chromium, molybdenum, and tungsten were prepared containing in the coordination sphere h 2 -and h 4 -molecules of 4-methyl-3-penten-2-one. Nonempirical methods were applied to calculation of the energy parameters of the coordinated molecules, and the factors governing the h 2 -and h 4 -coordination of the oxodiene system were established. A thermochemical study was performed on the 4-methyl-3-penten-2-one h 4 -coordination product with carbonyl metal core. A scheme of the thermal decomposition was suggested for the iron (0) h 4 -(4-methyl-3-penten-2-one)tricarbonyl.A development of new preparative procedures based on the chemo-, regio-, and stereoselective addition reactions is among the most prominent trends in the modern synthetic chemistry. The interest attracted by this field of the synthetic organic and organometallic chemistry originates from the maximum atomic efficiency and atom-saving [1] of the addition reactions, especially of those occurring strictly at the definite structural fragments of substrates.We showed formerly that conjugated oxo-and azadienes located in the coordination sphere of the transition metals were involved in dialkyl phosphines addition at the carbon-heteroatom double bond irrespective of the type of heterodiene coordination with the metal center [26].The equal reactivity of the coordinated heterodienes independent of hapticity of their bonding cannot be rationalized regarding the metal only as a protective group [36] since as we have established the bonding with the metal center results in significant changes in the geometry and electronic structure of the oxodiene ligand [7]. Obviously for successful intracomplex functionalizing of unsaturated molecules a detailed study is required on the factors governing the readiness of organometallic compounds formation and also on the thermal stability and reactivity of the unsaturated molecules within the coordination sphere of the transition metal.In the present study we approached these problems by investigation of reactions between the 4-methyl-3-penten-2-one (mesityl oxide) and iron(0) pentacarbonyl and hexacarbonyls of metals of VIB group under both photochemical and thermochemical activation.Under UV irradiation of a THF solution containing a homocarbonyl complex of a transition metal and mesityl oxide products were obtained of h 2 -coordination of aenone IaId. The p-type coordination of the olefin ligand with the metal atom was confirmed by the appearance in the IR spectra of the reaction products of the absorption bands of the C=C bond coordinated to a metal center: 1560 (Ia), 1565 cm 1 (Id); in a free mesityl oxide the corresponding band was observed at 1640 cm 1 . In the region of the stretching vibrations of the C=O bond of the carbonyl ligands coordinated to the metal in the spectrum of compound Ia were observed four, and in the spectra of compounds Ib-Id five well resolved bands revealing that only one molecule of carbon monoxide was replaced in...

Solid-state thermal degradation behaviour of 1-D coordination polymers of Ni(II) and Cu(II) bridged by conjugated ligand

“…The ν(C=C) and βNH 2 vibration modes of the ligand merge and yield a single broad band in the metal complexes except for 2 where ν(C= C) is observed as distinct shoulder at 1542 cm -1 and βNH 2 mode as very strong peak at 1494 cm -1 . Shifting of these bands to lower wavenumbers in the metal complexes as compared to that of the free ligand dadb value supports coordination through nitrogen and oxygen atoms of the ligand in monometallic as well as in heterobimetallic complexes [8,17,18].…”

“…In metal complexes of dadb the asymmetric (C=O) stretching vibrational mode is observed in the range 1610 -1655 cm -1 either as medium intensity shoulder or distinct peak. Thus lowering of ν(C=O) frequency in the metal complexes is in favour of coordinated nature of carbonyl group [18] of the ligand. The ν(C=C) and βNH 2 vibration modes of the ligand merge and yield a single broad band in the metal complexes except for 2 where ν(C= C) is observed as distinct shoulder at 1542 cm -1 and βNH 2 mode as very strong peak at 1494 cm -1 .…”

Synthesis of 1-(2-aminopyridine)-4-phenyl-1-azabuta-1,3-diene and 1-(3-aminopyridine)-4-phenyl-1-azabuta-1,3-diene as heterodienes for iron carbonyl complexes

“…Although a large number of p-(1,3-diene) iron tricarbonyl complexes have been reported and their reactivity investigated [1], less is known of the corresponding heterodiene compounds. In such compounds, which may be regarded as derived from the basic butadiene unit by the replacement of one or more of the carbon atoms by the oxygen or nitrogen, the possibility arises that the lone pair of electrons of the heteroatom is involved with the metal-ligand bond [2][3][4][5].In this study we report the synthesis of two new Schiff bases derived from 2-aminopyridine, 3-aminopyridine and cinnamaldehyde.These compounds are potentially good ligands for iron carbonyl complexes.…”