Ionic iron complex [(Me(3)tacn)(2)Fe(2)Cl(3)](+)[(Me(3)tacn)FeCl(3)](-) (1), which is readily soluble in methanol, acted as a powerful catalyst in controlled radical polymerization of styrene and MMA, and showed promising features of removal from the resulting polymers and was reusable after recovery from the crude products.

Novel synthetic methods for Ti−Mo, Ti−W, and Ti−Ru heterobimetallic complexes are established by the reaction of a certain titanium(III) alkoxide and the corresponding metal carbonyl dimer, [CpM(CO) n ]2 [M = Mo, W (n = 3); M = Ru (n = 2)]. Thus, a novel monomeric titanium complex, Cp2Ti(OtBu) (1), which is synthesized from Cp2TiCl and KOtBu and characterized by spectroscopy and crystallography, smoothly reacts with [CpM(CO)3]2 (M = Mo (2a), W (2b)) to give heterobimetallic complexes, Cp2Ti(OtBu)(μ-OC)M(CO)2Cp (M = Mo (3a) and W (3b)), of which two metallic moieties are linked by the isocarbonyl bridge. Similar reaction of 1 with [CpRu(CO)2]2 (4) does not occur thermally, but is accomplished under photoirradiation to afford Cp2(OtBu)Ti−Ru(CO)2Cp (5), of which two metallic moieties are linked by a direct metal−metal bond. Use of 1 is particularly important for these reactions; other titanium alkoxides such as [Cp2Ti(OMe)]2 and Cp2Ti[O(2,6-tBu2-4-Me)C6H2] do not react with the metal carbonyl dimers. An interesting feature of these new heterobimetallic complexes, 3a, 3b, and 5, is the existence of the thermal fragmentation process to regenerate the starting materials:  3a or 3b is actually in equilibrium with a mixture of 1 and 2a or 1 and 2b, respectively [ΔG 0 298K = −4.1 ± 0.2 kcal mol-1 (3a), −4.3 ± 0.2 kcal mol-1 (3b)]. The Ti−Ru compound 5 thermally undergoes fragmentation to regenerate 1 and 4. The formation of these heterobimetallic complexes is formally considered as the metal−metal bond cleavage of metal carbonyl dimers by a Ti(III) reducing reagent; possible mechanisms are discussed.

Reactions of titanium(III) complexes (η5-C5R5)2TiOtBu (R = H (1), Me (4)) with Co2(CO)8 are found to be efficient methods to synthesize Ti−Co heterobimetallic complexes. A Ti−Co3 complex, (η5-C5H5)2Ti(OtBu)(μ4-OC)Co(CO)9 (3), was formed from 1 and Co2(CO)8, whereas a Ti−Co bimetallic complex, (η5-C5Me5)2Ti(OtBu)(μ-OC)Co(CO)3 (5), was obtained by the reaction of 4 with Co2(CO)8. In both cases, the reaction was complete within 5 min. The products were completely characterized by NMR, IR, and X-ray crystallography. Complex 3 contains a quadruply bridging CO group, the oxygen terminus of which is connected to the Ti moiety, whereas the carbon terminus is bound to three Co atoms in the Co3(CO)9 moiety. In contrast, complex 5 is dinuclear, and its Ti atom is connected to the Co(CO)3 group by an isocarbonyl bridge. A η5-C5H5 analogue of 5, [(η5-C5H5)2Ti(OtBu)(μ-OC)Co(CO)3] (6), was formed at the initial stage of the reaction of 1 with Co2(CO)8 in toluene. This dinuclear complex 6 was isolated from a reaction medium of a 5:1 mixture of 1 and Co2(CO)8, being characterized by spectroscopy. As further evidence for the formation of the Ti−Co heterobimetallic complex, reaction of 6 with THF gave the Ti−Co complex [(η5-C5H5)2Ti(OtBu)(η-THF)]+[Co(CO)4]- (7), which was completely characterized by spectroscopy, crystallography, and elemental analysis. Thermal decomposition of 6 produced a mixture of 3 and 1, whereas treatment of 6 with Co2(CO)8 gave 3; this is good evidence for the intermediacy of 6 in the formation of 3 from 1 with Co2(CO)8.

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The haptotropic rearrangement of diiron carbonyl species on the conjugate π-ligand in (µ 2 ,η 3 :η 5 -acenaphthylene)Fe 2 (CO) 5 (1) and its analogue (µ 2 ,η 3 :η 5 -aceanthrylene)Fe 2 (CO) 5 ( 2) is investigated in both solution and solid states. The diiron complexes 1 and 2 have two isomers, and each isomer is isolated and characterized. Isomers 1-A and 2-A are thermodynamically more stable than 1-B and 2-B, respectively (∆G°2 96 ) 2.3 kcal/mol for 1; ∆G°2 96 > 2.3 kcal/mol for 2). The thermodynamically less stable isomers can be prepared photochemically. Interconversions between 1-A and 1-B and between 2-A and 2-B occur both thermally and photochemically. Kinetic studies on the thermal isomerizations in solution provide ∆G q 298 ) 23 ( 1 kcal/mol, ∆H q 298 ) 23 ( 1 kcal/mol, and ∆S q 298 ) 1 ( 4 cal/mol‚deg for the reaction of 1-B to 1-A, and ∆G q 298 ) 26 ( 1 kcal/mol, ∆H q 298 ) 26 ( 1 kcal/mol, and ∆S q 298 ) 0 ( 2 cal/mol‚deg for the reaction of 2-B to 2-A. Photochemical interconversion at λ ) 600 nm provides the isomer ratio of 1-A:1-B ) 9:91 at the photostatic state, and 2-A: 2-B ) 66:34. In both of the isomerization reactions, irradiation with light of shorter wavelength tends to give lower ratios of the thermodynamically less stable isomers. The quantum yields of the isomerization reactions are found to be Φ 1-Af1-B ) 0.30(3), Φ 1-Bf1-A ) 0.09(1), Φ 2-Af2-B ) 0.013(2), and Φ 2-Bf2-A ) 0.009(1). From these experimental data the reaction mechanisms of the thermal and photochemical haptotropic rearrangements are discussed with the aid of EHMO calculations. A single crystal of 1-B converts to a single crystal of 1-A upon heating. A photolysis (5 min by a 500 W xenon lamp)/thermal treatment (10 min at 100 °C) cycle of a KBr pellet containing 1-A or 1-B results in reversible interconversion between 1-A and 1-B in the solid state, which can be monitored by the IR absorption at ν ) 1825 cm -1 . The cycle is repeatable for over 10 times without change in the signal intensity. These results are the first to indicate a possible organometallic photochromism in the solid state detectable by the IR light.