Cationic complexes of iridium: diiodobenzene chelation, electrophilic behavior with olefins, and fluxionality of an Ir(I) ethylene complex.

The synthesis of a series of dicationic Ir(III) complexes is described. Reaction of Ir(CO)(dppe)I (dppe = 1,2-bis(diphenylphosphino)ethane)) with RI (R = CH(3) and CF(3)) results in formation of the Ir(III) precursors IrR(CO)(dppe)(I)(2) (R = CH(3) (1a) and CF(3) (1b)). Subsequent treatment with AgOTf (OTf = triflate) generates the bis(triflate) analogues IrR(CO)(dppe)(OTf)(2) (R = CH(3) (2a) and CF(3) (2b)), which undergo clean metathesis with NaBARF (BARF = B(3,5-(CF(3))(2)C(6)H(3))(4)(-)) in the presence of 1,2-diiodobenzene (DIB) forming the dicationic halocarbon adducts [IrR(CO)(dppe)(DIB)][BARF](2) (R = CH(3) (3a) and CF(3) (3b)). Complexes 3a and 3b demonstrate facile exchange chemistry with acetonitrile and carbon monoxide forming complexes 4 and 5, respectively. NMR investigation of the mechanism reveals that the process proceeds through an eta(1)-diiodobenzene adduct, where labilization at the coordination site trans to the alkyl group occurs first. Complex 3a reacts with ethylene forming the cationic iridium(I) product [Ir(C(2)H(4))(2)(CO)(dppe)][BARF] (6), which demonstrates fluxional behavior. Variable-temperature NMR studies indicate that the five-coordinate complex 6 undergoes three dynamic processes corresponding to ethylene rotation, Berry pseudorotation, and intermolecular ethylene exchange in order of increasing temperature based on NMR line shape analyses used to determine the thermodynamic parameters for the processes. The DIB adducts 3a and 3b were also found to promote olefin isomerization of 1-pentene, and polymerization/oligomerization of styrene, alpha-methylstyrene, norbornene, beta-pinene, and isobutylene via cationic initiation.

Dipyridocatecholate-Bridged Complexes of Platinum and Ruthenium Diimine Chromophores.

New Ru-Pt heterometallic complexes have been prepared and their electrochemical and luminescence properties characterized. One series of complexes contains a tris diimine-chelated Ru(II) center linked to one, two, or three Pt(II) diimine moieties via a dipyridocatecholate (dpcat; 1,10-phenanthroline-5,6-diolate) bridging ligand, as indicated by the general formula [(dbbpy)(3)(-)(n)()Ru((&mgr;-dpcat)Pt(dbbpy))(n)()](PF(6))(2) (n = 1-3) where dbbpy = di-tert-butylbipyridine. A different dinuclear complex has a tetrapyridophenazine (tppz) bridge connecting a Ru(diimine)(3)(2+) chromophore with a Pt diimine dithiolate center and has the formula [(dbbpy)(2)Ru(&mgr;-tppz)Pt(tdt)](2+) where tdt = toluene-3,4-dithiolate. The dpcat-bridged complexes exhibit numerous redox processes that are assigned on the basis of comparison of those shown by mononuclear precursors and analogues, i.e., Ru(diimine)(3)(2+) and Pt(dbbpy)(dpcat). The dpcat-bridged complexes display distinct absorption bands due to Ru(diimine)(3)(2+) and Pt(diimine)(diolate) chromophores at ca. 450 and 540 nm, respectively. Emission from the Pt center is observed at 77 K (but not at room temperature in fluid solution) upon direct irradiation of this center as well as excitation of the Ru center. The latter suggests the occurrence of energy transfer between Ru- and Pt-based components. The energy transfer appears to be efficient, but not complete for the dinuclear species [(dbbpy)(2)Ru(&mgr;-dpcat)Pt(dbbpy)](PF(6))(2), as indicated by residual Ru emission from this complex. In contrast with the observation of a Pt-based emission from the bridged dinuclear complexes, the mononuclear complex Pt(dbbpy)(dpcat) does not luminesce, even in rigid media at low temperature. The spectroscopic properties of the tppz-bridged complex [(dbbpy)(2)Ru(&mgr;-tppz)Pt(tdt)](2+) are very similar to those of [(dbbpy)(2)Ru(&mgr;-dpcat)Pt(dbbpy)](2+).

Synthesis, Characterization, and Spectroscopy of Dipyridocatecholate Complexes of Platinum.

Several new complexes containing 1,10-phenanthroline-5,6-diolate (dipyridocatecholate, dpcat(2)(-)) ligand are reported. The complex (dpcat)Pt(dbbpy) (4; dbbpy = di-tert-butylbipyridine) was synthesized from Cl(2)Pt(dbbpy) and dpcat(2)(-). The reaction of (dpcat)Pt(dbbpy) with Cl(2)Pt(PhCN)(2) yielded Cl(2)Pt(dpcat)Pt(dbbpy) (5). The latter complex was reacted with 3,4-dimercaptotoluene (toluenedithiolate, tdt(2)(-)), 3,5-di-tert-butylcatecholate (dbcat(2)(-)), and dpcat(2)(-) to give (tdt)Pt(dpcat)Pt(dbbpy) (6), (dbcat)Pt(dpcat)Pt(dbbpy) (7), and (dpcat)Pt(dpcat)Pt(dbbpy) (8), respectively. All of these complexes containing Pt(diimine)(diolate) centers display intense absorption bands in the 500-600 nm range. However, excitation at these wavelengths does not result in photoemission similar to that seen for closely related Pt(diimine)(dithiolate) complexes. The absorption bands of the dinuclear species are unsymmetrical, possibly indicating isolated but overlapping transitions for the two chromophores in each complex. The complex (dpcat)Pt(dbbpy) was found to react with (dbbpy)(2)RuCl(2) and NH(4)PF(6) to yield [(dbbpy)(2)Ru(dpcat)Pt(dbbpy)](PF(6))(2) (10). A connectivity structure of this compound confirms the structural arrangement and the role of dpcat as a bridging ligand between a square planar Pt(II) center and an octahedral Ru(II) moiety. In an analogous synthesis, the trinuclear complex [(dbbpy)(2)Ru(dpcat)Pt(dpcat)Pt((dbbpy)](PF(6))(2) (11) was obtained by reacting (dpcat)Pt(dpcat)Pt(dbbpy) with (dbbpy)(2)RuCl(2) and NH(4)PF(6). The complex [(dbbpy)(2)Ru(dpcat)Pt(dbbpy)](PF(6))(2) displays absorption bands associated with individual Ru and Pt centers and photoemission that arises from Ru(diimine)(3)(2+). A trinuclear complex (dbcat)Co{(dpcat)Pt(dbbpy)}(2) (9) was also obtained from the reaction of (dpcat)Pt(dbbpy) and Co(4)(dbsq)(8) (dbsq = di-tert-butylsemiquinone).