Alkene insertion reactions of nitrogen-coordinated acylpalladium(II) complexes : the X-ray structure of the dicyclopentadiene insertion product [Pd(C20H23COMe)(bpy)]SO3CF3

The new acylpalladium(II) complex [PdI(COMe)(bpy)] (2b, bpy = 2, 2'-bipyridyl) has been obtained by two routes; (i) by insertion of carbon monoxide into the Pd@?C bond of [PdIMe(bpy)] (1b), and (ii) by ligand exchange from [PdI(COMe)(tmeda)] (2a, tmeda = N,N,N',N'-tetramethylethanediamine). The cationic species obtained by reaction of 2a and 2b with AgOSO{2}CF{3} both undergo alkene insertions into the Pd@?C acyl bond that lead to remarkably stable products. The X-ray structure of the dicyclopentadiene insertion product [Pd(C{1}{0}H{1}{2}COMe)(bpy)]SO{3}CF{3} (4b) shows the oxygen atom of the carbonyl group to be coordinated to the metal center (Pd@?O = 2.026(3) @9)

Alkylidene-centered rearrangement of a tantalum alkylidene alkoxide species with the N,C,N,-bis-ortho-chelated 1,2,6-trisubstituted aryldiamine ligand [C6H3(CH2NMe2)2-2,6]- to a product with a C,N-mono-ortho-chelated 1,2,4-trisubstituted aryldiamine ligand. X-ray molecular structure of [TaCl(=Ch-t-Bu){C6H3(CH2NMe2)2-2,4}(O-t-Bu)]

The reaction of 2 equiv of LiO-t-Bu with [TaCl2(=CH-t-Bu){C6H3(CH2NMe2)2-2,6}] (1), in which there is an N,C,N-chelated 1,2,6-trisubstituted aryldiamine ligand, affords in a one-pot procedure at 80 C the new rearranged product [Ta(=CH-t-Bu){C6H3(CH2NMe2)2-2,4}(O-t-Bu)2] (2), in which there is a C,N-chelated 1,2,4-trisubstituted aryldiamine ligand. Complex 2 is a yellow solid that has been isolated in 69% yield. The reaction mechanism for the formation of 2 involves a crucial isomerization of the intermediate [TaCl(=CH-t-Bu){C6H3(CH2NMe2)2-2,6}(O-t-Bu)] (3) to the rearranged intermediate [TaCl(=CH-t-Bu){C6H3(CH2NMe2)2-2,4}(O-t-Bu)] (4). The intermediate complexes 3 and 4 have been independently prepared and characterized. The known complex 3 can be obtained by reaction of 1 with LiO-t-Bu at room temperature. Complex 4 is obtained exclusively, as revealed by 1H NMR spectroscopy, by heating a benzene solution of 3 to 80 C and has been isolated as a purple solid in 77% yield. In solution 4 exists as two rotational isomers for the Ta=C(H)-t-Bu moiety; G = 71 kJ mol-1. The X-ray molecular structure of 3 shows it to be a pentacoordinate Ta(V) species in which the aryl Cipso atom, the alkylidene functionality, and the alkoxide group define the meridional plane of a trigonal bipyramid, with one of the NMe2 nitrogen donors of the C,N-bidentate-bonded aryldiamine and the chloride occupying the axial positions. The lone pair of the N-donor atom of the second ortho amine substituent is oriented toward Ta (Ta···N = 2.629.4 Å), providing incipient 3(N,C,N) facial bonding of the aryldiamine ligand. The structure of 3 also shows a pseudo-parallel orientation of the alkylidene C-H bond and the Cipso-Ta bond that points to potential C-H activation via a four-membered metallacyclic ring that contains Ta, Cipso, C, and H. The involvement of the alkylidene functionality in the sequence of highly regiospecific C-H bond-making and -breaking processes necessary to produce complex 4 from 3 was confirmed by deuterium-labeling experiments. The mechanism probably involves an -H abstraction from the alkylidene moiety in 3 (assisted by the weakly coordinated dimethylamino group) that leads to an intermediate which has a geometry similar to that of a known aryltantalum(V) zinc alkylidene adduct

Synthesis of methyltrioxorhenium(VII) arylamine complexes and mono- and bis(ortho)-chelated arylaminorhenium(VII) trioxides

From the reaction of MeReO{3} with the neutral arylamine C{6}H{5}CH{2}NMe{2} and the aryldiamine C{6}H{4}(CH{2}NMe{2}){2}-1, 3, have been isolated in good yields the 1/1 adduct complex [MeReO{3}.C{6}H{5}CH{2}NMe{2}], 1, and the21 adduct complex [(MeReO{3}){2} . C{6}H{4}(CH{2}NMe{2}){2}-1,3], 2, respectively. The X-ray molecular structure of 2 shows that both rhenium centres have a trigonal bipyramidal geometry and in the axial positions of each rhenium centre are one of the NMe{2} units of the aryldiamine ligand and a methyl group. The mono(ortho)-chelated arylaminorhenium trioxide complex [ReO{3}{C{6}H{4}CH{2}NMe{2}-2}], 3, can be synthesized by a transmetallation reaction of ClReO{3} with [Zn{C{6}H{4}CH{2}NMe{2}-2}{2}] in a 2:1 molar ratio. In a similar way the bis(ortho)-chelated arylaminorhenium trioxide complex [ReO{3}{C{6}H{3}(CH{2}NMe{2}){2}-2,6}], 4, can be synthesized by addition of a mixture of [Li{2}{C{6}H{3}(CH{2}NMe{2}){2}-2,6}{2}] and ZnCl{2} to ClReO{3}. Complexes 3 and 4 have been isolated as white solids in 66% and 81% yields respectively. The rhenium centre in complex 4 has a bicapped tetrahedral geometry in which the monoanionic {C{6}H{3}(CH{2}NMe{2}){2}-2,6}}-{ ligand is pseudo-facially bonded with a characteristic N1-Re-N2 angle of 107.7(3)}o{, a Re-C{i}{p}{s}{o} bond length of 2.112(11) @?9 and Re-N1 and Re-N2 bond lengths of 2.518(9) @?9 and 2.480(8) @?9 respectively

Synthesis and reactivity of tantalum alkylidene complexes containing the C,N,N'-chelating aryldiamine ligand [C6H4(CH2N(Me)CH2CH2NMe2)-2- (CNN). X-ray structurs of [TaCl2(=CH-t-Bu) (CNN)], [Ta{CH2)3-1,3}(CNN)(O-t-Bu)2], and [Ta(CNN)(O-t-Bu)2(H2C=CH2)]

The potentially C,N,N'-chelating anionic aryldiamine ligand [C6H4(CH2N(Me)CH2CH2NMe2)-2]- (CNN) has been employed in the preparation of six-coordinate Ta(V) alkylidene complexes. The new dichloro alkylidene complex [TaCl2(=CH-t-Bu)(CNN)], 2, prepared from [TaCl3(=CH-t-Bu)(THF)2] and [Li(CNN)]2, 1, has been obtained as a mixture of three diastereoisomers (2a-c) in 51% yield. The molecular structure of the major isomer 2a, determined by X-ray methods, shows this to be a tetragonal bipyramidal complex in which the metal coordination sphere is comprised of the C,N,N' facially bonded CNN, two cis-positioned chlorides in the equatorial plane, and a neopentylidene group and the NMe2 nitrogen donor mutually trans-positioned at the apices. The dialkoxide complexes [Ta(=CHR)(CNN)(O-t-Bu)2] (R = t-Bu (3a), CMe2Ph (3b)) have been obtained by transmetallation of [TaCl(=CHR)(O-t-Bu)2(PMe3)] with 1. The neopentylidene complex 3a was isolated as an analytically pure orange solid in 47% yield, whereas the neophylidene complex 3b was isolated as an orange oil of ±90% purity. Complex 3b reacts in pentane with ethene at room temperature to afford the tantalacyclobutane complex [Ta{(CH2)3-1,3}(CNN)(O-t-Bu)2], 4, which was isolated as a white solid in 81% yield. An X-ray diffraction study of 4 shows it to be a heptacoordinate pentagonal bipyramidal tantalum species in which two mutually trans alkoxide groups are in the apical positions; the meridional ligation is comprised of the C,N,N'-coordination of CNN and the -bonded carbon atoms of the metallacyle. Reaction of 3b in hexane at 69 C with ethene gives a mixture of the new tantalum alkene complex [Ta(CNN)(O-t-Bu)2(H2C=CH2)], 5, and 4 in a 5:2 ratio. Complex 5 can be isolated from this mixture as a yellow solid by recrystallization from diethyl ether at -30 C. The X-ray molecular structure of 5 shows it to be a pentagonal bipyramidal complex in which the array of atoms directly bonded to tantalum is like that in 4. However, in 5, the meridional ligation is comprised of the C,N,N'-coordination of CNN and the two C atoms of the ethene molecule. Complexes 3b and 4 initiate ring-opening metathesis polymerization with strained cyclic olefins; dicyclopentadiene produces cross-linked polymers, whereas norbornene produces polycyclopentamers with approximately 90% trans-vinylene bonds. In contrast, none of the isomers of alkylidene complex 2 show any reactivity toward either ethene or norbornene