C.T. Mortimer

Platinumolefin bond strength in Pt(PPh3)2(CH2CH2) and Pt(PPh3)2 {C(CN)2C(CN)2}

Abstract The enthalpy of the reaction: Pt(PPh 3 ) 2 (CH 2 CH 2 )(cryst.) + C(CN) 2 C(CN) 2 (g) → Pt(PPh 3 ) 2 {C(CN) 2 C(CN) 2 }(cryst.) + CH 2 CH 2 (g) has been determined as Δ H 298 =−155.8±8.0 kJ·mol −1 , from solution calorimetry. The interpretation, that the platinumethylene bond is much weaker than the platinumtetracyanoethylene bond, is contrary to conclusions drawn recently from electron emission spectroscopic studies, but in agreement with available structural data.

The thermal decomposition of transition-metal complexes containing heterocyclic ligands: 3. Substituted pyridine complexes of cobalt

Abstract Enthalpies of the overall decomposition reactions CoX 2 L 2 (c) → CoX 2 (c)+2L(g) and of the intermediate stepwise loss of ligand, L, where X is Cl or Br, and L is 3-chloropyridine, 3-bromopyridine, 2-chloropyridine, 2-bromopyridine, or 2-methoxypyridine have been measured by use of a differential scanning calorimeter. Enthalpies of sublimation of CoCl 2 (3-chloropyridine) 2 , CoBr 2 (3-chloropyridine) 2 , CoCl 2 (3-bromopyridine) 2 , CoCl 2 (2-chloropyridine) 2 , CoCl 2 (2-bromopyridine) 2 , CoBr 2 (2-bromopyridine) 2 , CoCl 2 (2-methylpyridine) 2 and CoBr 2 (2-methylpyridine) 2 have been determined. Values of the cobalt-nitrogen bond dissociation energies have been calculated. Specific heats of a number of the complexes are reported.

The platinium—carbon bond strength in Pt(PPh3)2(CPhCPh)

Abstract The enthalpy of the reaction: Pt(PPh3)2(CH2CH2)(cryst.) + CPhCPh(cryst.) → Pt(PPh3)2(CPhCPh)(cryst.) + CH2CH2(g) has been determined as /gDH298 = −82 ∓ 12 kJ mol−1, from solution calorimetry. The conclusion, that the platinum—tolane bond is stronger than the platinum—ethylene bond, is in agreement with available structural data.

Strength of iridium-olefin and iridium-acetylene bonds

Abstract Enthalpies of the dissociation reactions: IrX(CO)(PPh 3 ) 2 (L)(cryst.) → IrX(CO)(PPh 3 - ) 2 (cryst.) + L(g) (X = F, Cl, Br, or I; L = C 2 F 4 or C 4 F 6 ) have been measured. These enthalpies decrease to a minimum value at X = Br, indicating an order of stability of F > Cl > Br > I.

The platinumcarbon bond strength in Pt(PPh3)2(CH3)I

Abstract The enthalpies of reaction 1–3 have been determined as Δ H (1) = −176.6 ± 5.4, Δ H (2) = −107.8 ± 6.0, and Δ H (3) = −78.9 ± 2.0 kJ mol −1 . The bond dissociation energy difference D 1 (PtCH 3 ) − D 1 (PtI) = +6 ± 5 kJ mol −1 is calculated, which indicates that the two bonds have very similar strengths.

Standard enthalpies of formation and sublimation of some crystalline bis(8-hydroxyquinolate) metal complexes

Abstract Resulting from a collaboration among three departments, the standard enthalpies of formation of some crystalline bis(8-hydroxyquinolate) metal complexes were determined by reaction-solution calorimetry. Enthalpies of hydrolysis were measured for several samples of each complex using various acidic solvents. 8-hydroxyquinoline is written as Hox. At 298.15 K, Δ f H θ m (M(ox) 2 ,cr)/(kJ mol −1 ) values are: Mg(ox) 2 , −516.0 ± 4.0; Ca(ox) 2 , −607.7 ± 4.4; Sr(ox) 2 , −585.9 ± 4.1; Ba(ox) 2 , −573.4 ± 4.5; Cu(ox) 2 , −103.3 ± 3.3; Zn(ox) 2 , −271.5 ± 3.6; Cd(ox) 2 , −179.6 ± 4.3; Pb(ox) 2 , −145.3 ± 3.8; Mn(ox) 2 , −307.1 ± 3.7; Fe(ox) 2 , −219.7 ± 4.5; Co(ox) 2 , −160.4 ± 4.2; Ni(ox) 2 , −165.5 ± 5.6. Where feasible, standard enthalpies of sublimation at 298.15 K were determined by measuring vapour pressures as functions of temperature. Δ g cr H θ m (M(ox) 2 )/(kJ mol −1 ) values are: Mg(ox) 2 , 230.2 ± 4.0; Cu(ox) 2 , 168.7 ± 7.3; Zn(ox) 2 , 183.2 ± 6.3; Cd(ox) 2 , 201.7 ± 7.5; Pb(ox) 2 , 187.1 ± 6.2; Mn(ox) 2 , 194.6 ± 10.4; Co(ox) 2 , 205.3 ± 4.0; Ni(ox) 2 , 175.4 ± 6.7. From the standard enthalpies of formation in the gaseous state, the mean metal-ligand dissociation enthalpies were derived and compared with corresponding values for other complexes of these metals.

The thermal decomposition of transition-metal complexes containing heterocyclic ligands: 2.Benzoxazole complexes

Abstract Enthalpies of the overall decomposition reactions and of the intermediate reactions involving stepwise loss of ligand, L, where M is Mn, Co, Ni, Cu, or Cd, X is Cl or Br, and L is benzoxazole, 2-methylbenzoxazole, or 2,5-dimethylbenzoxazole have been measured by use of a differential scanning calorimeter. Specific heats of CoCl 2 (2-methylbenzoxazole) 2 , and CoBr 2 (2-methylbenzoxazole) 2 are reported together with enthalpies of sublimation of CoCl 2 (2-methylbenzoxazole) 2 , CoBr 2 (2-methyl-benzoxazole) 2 , CoCl 2 (2,5-dimethylbenzoxazole) 2 and CoBr 2 (2,5-dimethylbenzoxazole) 2 . Enthalpies of decomposition of benzoxazole complexes are found to be greater than those of the corresponding pyridine complexes, but less than those of the analogous benzothiazole complexes. However, the mean bond dissociation energies of the cobalt—nitrogen and cobalt—oxygen bonds in these complexes are all in the region 33±2 kcal mol − .

The thermal decomposition of transition—metal complexes containing heterocyclic ligands: 4. Substituted—pyridine complexes of Mn, Ni, Cu and Cd

Abstract Enthalpies of the overall decomposition reactions MX 2 L 2 (c) → MX 2 (c) + 2L(g) and of the intermediate stepwise loss of ligand, L, where X is Cl or Br; L is 3-chloropyridine, 3-bromopyridine, 2-chloropyridine, 2-bromopyridine, or 2-methoxypyridine; and M is Mn, Ni, Cu, or Cd have been measured by use of a differential scanning calorimeter. Enthalpies of sublimation of NiCl 2 (3-chloropyridine) 2 , NiCl 2 (3-bromopyridine) 2 and CuCl 2 (3-bromopyridine) 2 have been determined. Values of the metal—nitrogen bond dissociation energies in these compounds have been calculated. A value for the specific heat of CuCl 2 (2-chloropyridine) 2 is reported.

Enthalpy of combustion of triphenylarsine oxide

Abstract The standard enthalpy of combustion of triphenylarsine oxide has been measured by use of a rotating-bomb combustion calorimeter. The enthalpy of formation, Δ H XXX f (Ph 3 AsO, c) = 18.8 ± 3.5 kcal mol − has been calculated, from which the bond dissociation energy D (Ph 3 As  O) =102.6 ± 7.3 kcal mol − has been obtained.

Enthalpies of reaction of bis(triphenylphosphine)(trans-stilbene)platinum(0) with diphenylcyclopropenone and benzocyclobutenedione

Abstract Enthalpies, ΔH(1) −94.8 ± 6.0 and ΔH(6) −57.1 ± 5.1 kJ mol−1, of the following reactions have been measured calorimetrically [Pt(trans-stilbene)(PPh3)2](s) + dpcp(g) → (PPh3)2Pt(dpcb)(s) + trans-stilbene(g) (1) [Pt(trans-stilbene)(PPh3)2](s) + bcbd(g) → (PPh3)2Pt(bcpd)(s) + trans-stilbene (g) (6) where dpcp is diphenylcyclopropenone, (PPh3)2Pt(dpcb) is (1,1-bistriphenylphosphine)platinadiphenylcyclobutenone, (PPh3)2 PtC(Ph)C(Ph)C O, bcbd is benzocyclobutene-1,2-dione and (PPh3)2Pt(bcpd) is (1,1-bistriphenylphosphine)platinabenzocyclopentanedione, . It is concluded that the five-membered platinacyclo ring system in (PPh3)2Pt(dpcb) is not heavily strained.