“…It is far greater than that found in three-membered metallacycles of the type which usually have values ranging from δ P +15.0 to −60.0, e.g. δ P +13.0 and +13.5 for Mn and Fe species, respectively (Table , entries 6 and 7), and δ P −57.4 for Somewhat higher shieldings occur in analogous dimethylphosphino complexes of 5d elements; e.g., for the δ value is −71.0 . However, a pronounced shielding occurs when the carbon atom of the phosphametallacyclopropane is part of a double bond.…”
The η 2 -alkynylphosphine complexes [Ni(η 2 -Ph 2 PCtCR)(dcpe)] (R ) Me (1a), CO 2 Me (1b), Ph (1c)), which are formed by displacement of ethylene from [Ni(C 2 H 4 )(dcpe)] by the corresponding alkynylphosphine, react with HCl (1 equiv) to give five-coordinate nickel(II) complexes, [NiCl{C(dCHR)PPh 2 -κP,C 1 }(dcpe)] (R ) Me (2a), CO 2 Me (2b), Ph (2c)), which contain a coordinated methylenephosphanickelacyclopropane fragment. In the case of 1a, the proton adds regiospecifically at the carbon atom bearing the methyl group. This mode of addition is favored for 1b,c, but small amounts of the addition products [NiCl{η 1 -C(R)d CH(PPh 2 )}(dcpe)] (R ) CO 2 Me (3b), Ph (3c)), arising from addition at the PPh 2 -bearing carbon atoms, are also formed. Unsaturated molecules such as CS 2 and CO 2 insert into the Ni-P bonds of complexes 2a,c to give five-membered nickelacycles. Complexes 1a, 2a,c, and 3c have been structurally characterized by X-ray diffraction analysis.
“…It is far greater than that found in three-membered metallacycles of the type which usually have values ranging from δ P +15.0 to −60.0, e.g. δ P +13.0 and +13.5 for Mn and Fe species, respectively (Table , entries 6 and 7), and δ P −57.4 for Somewhat higher shieldings occur in analogous dimethylphosphino complexes of 5d elements; e.g., for the δ value is −71.0 . However, a pronounced shielding occurs when the carbon atom of the phosphametallacyclopropane is part of a double bond.…”
The η 2 -alkynylphosphine complexes [Ni(η 2 -Ph 2 PCtCR)(dcpe)] (R ) Me (1a), CO 2 Me (1b), Ph (1c)), which are formed by displacement of ethylene from [Ni(C 2 H 4 )(dcpe)] by the corresponding alkynylphosphine, react with HCl (1 equiv) to give five-coordinate nickel(II) complexes, [NiCl{C(dCHR)PPh 2 -κP,C 1 }(dcpe)] (R ) Me (2a), CO 2 Me (2b), Ph (2c)), which contain a coordinated methylenephosphanickelacyclopropane fragment. In the case of 1a, the proton adds regiospecifically at the carbon atom bearing the methyl group. This mode of addition is favored for 1b,c, but small amounts of the addition products [NiCl{η 1 -C(R)d CH(PPh 2 )}(dcpe)] (R ) CO 2 Me (3b), Ph (3c)), arising from addition at the PPh 2 -bearing carbon atoms, are also formed. Unsaturated molecules such as CS 2 and CO 2 insert into the Ni-P bonds of complexes 2a,c to give five-membered nickelacycles. Complexes 1a, 2a,c, and 3c have been structurally characterized by X-ray diffraction analysis.
“…The target molecules were prepared by treatment of the known cyclometalated complex L 3 Os(H)( η 2 -CH 2 PMe 2 ) with the appropriate aromatic precursor (eq 1). Acid cleavage reactions of this complex are well-known. 4a,, The relative reactivities of the arenes parallel their acidities in that 2-mercaptopyridine reacts within 5 min at ambient temperature, pyridone requires about 20 min at 80 °C, and 2-aminopyridine requires heating at 80 °C for 40 h for complete reaction. …”
Ring opening of a strained chelate complex of osmium has been investigated as a means to transient coordinative unsaturation under mild conditions in normally kinetically inert, third-row, platinum-group metals. cis-L 4 Os(H)(NC 5 H 4 X) (L ) PMe 3 ; X ) O (1), NH (2), S (3)) were prepared by treatment of fac-L 3 Os(H)(η 2 -CH 2 PMe 2 ) with 2-(HX)C 5 H 4 N. An X-ray structure determination establishes 1 to be the κN tautomer with the keto group pointed away from the hydride and toward the PMe 3 ligand trans to hydride. NMR spectra support the κN structure in solution. Which nitrogen is coordinated in 2 is not established, but NMR supports the κS tautomer of 3 in solution. At 80 °C in C 6 D 6 , 1 incorporates L′ (P(CD 3 ) 3 ) in a first-order reaction (t 1/2 ≈ 14 min) stereospecifically at site b (trans to hydride) with ∆H q ) 26.9 ( 1.4 kcal/mol and ∆S q ) 3.8 ( 4.4 eu for the substitution. Complex 2 at 80 °C also exchanges with L′ only in site b, but more slowly than 1 (t 1/2 ≈ 3.5 h). Sublimation of 1 at 55 °C under vacuum yields mer-L 3 Os(H)(NC 5 H 4 O-κ 2 N,O) (mer-4), believed to have mer-4-(HON) geometry (H trans to nitrogen). In toluene at reflux 1 loses L, forming fac-4. Heating mer-4 in benzene 3 h at 110 °C forms fac-4. At 22 °C, L′ adds to fac-4 withReaction of mer-4 with excess L′ in ca. 2 h generates trans-L 3 L′Os(H)(NC 5 H 4 O) then trans-L′ 4 Os(H)(NC 5 H 4 O) over 10 h, and finally cis-L′ 4 Os(H)(NC 5 H 4 O-κN) over 10 days. A scheme is presented that correlates all of the above transformations. Several reactions of fac-4 were examined. fac-4 and CO 2 (10 atm, benzene-d 6 , 80 °C, 1 h) afforded fac-L 3 Os(κ 1 -O 2 CH)-(κ 2 -NC 5 H 4 O), 5. Heating pure 5 in C 6 D 6 (110 °C, 2 h) regenerated 4. Reaction of fac-4 with D 2 gas (0.84 atm, C 6 D 6 , 80 °C) caused formation of Os-D with no other changes. fac-4 in neat 1-hexene (80 °C, 17 h) gave fac-L 3 Os(n-hexyl)(κ 2 -NC 5 H 4 O) (6) quantitatively, while fac-4 under 1 atm of ethylene (C 6 D 6 , 80 °C, 36 h) gave fac-L 3 Os(ethyl)(κ 2 -NC 5 H 4 O) (7) quantitatively. Heating 6 in C 6 D 6 at 80 °C for 48 h gave fac-4 back again with a mixture of hexene isomers with a 2:1 terminal:internal alkene ratio. Heating 7 (C 6 D 6 , 80 °C) also regenerated 4 and ethylene. Heating at 80 °C for 7 days of a sample containing 1-hexene in C 6 D 6 solvent and 5 mol % of fac-4 under 1 atm of hydrogen gas quantitatively gave hexane, while 4 remained unchanged. This is a substantial increase in reactivity over L 4 Os(H) 2 through the use of the strained chelate.
“…It is quite clear why transition metal hydrides with different types of ligands have attracted so much attention over the past decade: compounds of this type have been successfully used in organometallic synthesis, catalysis, and photochemistry 5a, the formation of binuclear species, 6d, metallation, 6b, selective C−H bond activation of aromatic and saturated hydrocarbons, and alkene hydrogenation . This wide range of reactions has usually been mediated by hydrides of the transition metals with co-ligands such as Cp, Cp*, and PR 3 (Cp = C 5 H 5 ; Cp* = C 5 Me 5 ; R = Ph, Me, etc.)…”
The photolysis of a benzene solution of [Tp(Me2)IrH(2)(COE)], 1 (Tp(Me2) = hydrotris(3,5-dimethylpyrazolyl)borate, COE = Z-cyclooctene), in the presence of P(OMe)(3), gives the stable novel complex [Tp(Me2)IrH(C(6)H(5))(P(OMe)(3))], 3a. The photochemical syntheses of [Tp(Me2)IrH(2)(P(OMe)(3))], from 1 and P(OMe)(3) in diethyl ether, and [Tp(Me2)IrH(2)(CH(2)=CHCOO(t)Bu)], from 1 in tert-butyl acrylate, are also reported. The above reactions and several experiments using C(6)D(6) and P(OCD(3))(3) show that, in all cases, the primary photoproduct is the 16-electron, five-coordinate iridium(III) intermediate {Tp(Me2)IrH(2)}, 6a, produced by loss of COE from 1. The above experiments also allow the postulation of a mechanistic pathway for the formation of 3a which involves the oxidative addition of an aromatic C-H bond by 6a. Furthemore, the photochemical reaction of 1 in the presence of P(OCD(3))(3) shows that, under the reaction conditions used, oxidative addition of C-H bonds of P(OMe)(3) and of coordinated Tp(Me2)-ligands, presumably, to the intermediates 6a and {Tp(Me2)IrH(C(6)H(5))}, also occurs. Thus, coordinatively unsaturated iridium(III) species readily activate C-H bonds.
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