2-phenylpyridine cyclometalation

The methyl-substituted phenylpyridine cyclometallated Ir(III) complexes, Ir(ptpy)2(bpy)+ and Ir(mppy)2(bpy)+, have been prepared and investigated [103,104]. The UV-visible absorption properties of these complexes are similar to that of the nonsubstituted ppy complex, displaying charge transfer transitions in the 325-468 nm spectral region. The emission spectra are also similar to that of the nonsubstituted complex. At room temperature in fluid solvents they display an emission maximum at 595 nm, but in rigid matrix at 77 K a dual structured emission with maxima centered at 527 and 550 nm are observed. The luminescence lifetimes are very close to those of Ir(ppy)2(bpy)+ (Table 2). 

Scheme 18. Synthetic routes to cyclometalated Ru11 mediators (55). 2-Phenylimidazole reacts similar to 2-phenylpyridine (228).

For only four of these cyclometallated complexes has any chemistry been pursued, viz. the C2,N[ -2-phenylpyridine chelates 466 and 467, and the P,C-2-phospinobenzyl chelates 468 and 469, which were each treated with a series of electrophiles and monitored by aH and 31P NMR spectroscopy. All were unreactive toward Mel, BzBr, Phi, and p-BrC6H4OMe up to ambient temperature, while I2 and the chlorinating agent PhICl2 both induced decomposition.143... 

In this article the results of a detailed optical spectroscopic investigation of a series of related bis-cyclometalated Rh3+ and Ir3 + complexes of the general formula [M(CnN),NnN]+, M = Rh3+, Ir3+ (HCnN = 2-phenylpyridine or 2-(2-thienyl) pyridine NnN = 2,2 -bipyridine or ethylenediamine) are summarized. The nature of the lowest excited states of the compounds is... 

Phenylpyridine is arylated by using aryltin reagents such as Ph4Sn in the presence of a rhodium catalyst (Eq. 15) [21]. The use of a halogenated solvent is important for obtaining a satisfactory yield. Although the precise mechanism is not yet clear, it is likely that a cyclometalated intermediate participates. 

Related cyclometallated complexes [RuC1(C-N)(CO)2]2 (HC-N = 2-phenylpyridine,2552 JV-phenylpyrazole,2552 PhCH=NMe,2533 2-(2-thienyl)pyridine2554) can also be synthesized from [RuC12-(CO)3]2 and the appropriate ligand. 

Many different palladium complexes have been used to form chelates via cyclometalation. Li2PdCLi is preferred over PdCb for solubility reasons. Also commonly used are (PhCN)2PdCl2, Pd(OAc)2, Pd(02CCp3)2, and Pd(acac)2. Where amines are the donor atom, dozens of different ligand types have reacted to form five-membered C,N-chelates. These include Al,Al-dimethylbenzylamines (23) and 3,2 -dimethylene-2-phenylpyridines (24). 

The acidification of H2 may also be involved in hydrogenase action, where H2 is beheved to bind to an Fe(II) center. Isotope exchange between H2 and D2O is catalyzed by the enzyme see Nickel Enzymes Cofactors Nickel Models of Protein Active Sites Iron-Sulfur Proteins). Similar isotope exchange can also occur in H2 complexes. Oxidative addition to give a classical dihydride is also a common reaction. [W(H2)(CO)3(PCy3)2] is in equilibrium with about 20% of the dihydride in solution. This can lead to subsequent hydrogenolysis of M-C bonds as in the case of a cyclometallated phenylpyridine complex of Ir(III). ... 

Figure 14. Kb values, from intervalence measurements, on a log scale, as a function of the through-space metal-metal distance +, ruthenium bipyridylpolyene complexes (series 1) , ruthenium bis(terpyridyl) complexes (series 2) , ruthenium bis(cyclometallated) complexes, dipyridylbenzene family (series 3) , ruthenium bis(cyclometallated) complexes, phenylpyridine family (series 4) A, bis(ferrocenyl)polyenes (series 5). Additional measurements a, bis(cyclometallated) complexes, phenylpyridine family with diethynylanthracene as spacer b, bis(ferrocene) with three phenylene and four vinylene units as spacer c, bis[ruthenium(trisbipyridyl)] with five double bonds as spacer. Note that the Cp (dppe)Fe system bridged by octatetrayne (13 A, 0.32 eV) is outside the graph.

Many types of aromatic substrate are known to undergo a cyclometallation reaction when exposed to alkylpentacar-bonylmanganese complexes under thermal conditions. It is well established that the treatment of ligand appended arenes with alkylmanganesepentacarbonyl complexes can lead to the formation of [C,Y] heterochelates of Mn(CO)4 (Y being a two-electron donor ligand) (Equation 6). For instance, aromatic compounds such as W,W-dimethylbenzyl-amine, alkyl benzyl thioethers, 2-phenylpyridine, acetophenone, benzaldehyde, and diazobenzene can be readily... 

Cationic complexes of cyclometallated Ir (ppy)2 (ppy = 2-phenylpyridine) with chelated diimine ligands, such as bipyridines (bipy) and phenan-throlines (phen), have interesting phosphorescent properties with potential applications in electroluminescent devices. Such compounds show at rather high energy MLCT transitions (2,nax = 340-380 nm) from the [Ir° (ppy)2]-based HOMOs to the LUMOs based on the n -orbitals of the phen (or bipy) ligands. Thus, these complexes can be considered as push-pull molecules in which the Ir° (ppy)2 moiety acts as the donor and the diimine as the acceptor part. 

A simple cyclometallated species [57], which resembles in many respects the well known Ru(bpy) +, is Ru(bpy)2(ppy)+. It can be prepared from Ru(bpy)2Cl2 and 2-phenylpyridine in the presence of Ag+. Several articles [58-60] on this and on similar compounds of the general composition Ru(bpy)2(CAN)+ have been published. CAN are the following ligands ... 

Several closely related arylgold(III) complexes have also been formed in the course of cyclometalation processes. The reaction of substituted pyridine ligands such as 2-phenylpyridine or 2-benzylpyridines (denoted HL) with [AuCL ]- at ambient temperature... 

Intercalation of the luminescent cyclometalated [Pt(C6ANAN)(MeCN)]+ 46 (HC6ANAN=2,9-diphenyl-l,10-phenanthroline) and [Pt2(C1 ANAN)2(/U-dppm)]2+ 7b complexes into calf-thymus DNA leads to a dramatic enhancement of their photoluminescence [16d]. The intercalation is likely to prohibit the solvent-induced quenching process, which typically occurs at the coor-dinative unsaturated platinum site for the MLCT excited state. The DNA-in-tercalating platinum(II) complex, [Pt(dppz)(tNAC)]CF3S03 (dppz=dipyri-do[3,2-a 2, 3 -c]phenazine, fNACH=4-ferf-butyl-2-phenylpyridine) 47 similarly exhibits an increase in emission intensity at Amax 650 nm on addition of calf thymus DNA (Fig. 22) [46]. 

In a similar way the pinene-phenylpyridine H[46] was prepared. Thus upon treatment of 4,5-(/f,/f)-pinene-2-phenylpyridine H[46] with IrCls.SHaO, the HEXOL-type tetranuclear iridium complexes [Ir IrCl2(46)2 3] were obtained as two isomers (5.67ab) in a ratio of 5 3 (Scheme 5.25). Each complex can be described as an inner core of HEXOL-type [Ir(IrCl2)3] units and a surface of six chiral bidentate cyclometallated ligands (46). 

A series of iridium(III) complexes of the type Ir(L-L)3 have been prepared by reaction of a glycerol solution of Ir(acac)3 and L-L (2-arylpyridine or 2-aryl-l-qui-noline) in an open vessel equipped with a reflux condenser. 5 This represented an improvement on the analogous methodology using a domestic microwave oven as less ligand was required, but YIFs were only 0.82-1.2. In the case of 2-phenyl-l-quin-oline, a 10% yield of the Ir complex was obtained in 20 min, while only trace amounts were produced after 10 h of conventional reflux. Cyclometallated platinum(II) complexes of the type PtCl(L-L)L where L-L = 2-phenylpyridine, 2-(2 -thienyl)pyridine, or benzoquinoline have also been prepared but not with any enhancement in yield (YIF = 0.58-1.0). 55... 

Ir(iii) complexes with nonconjugated l-[(diphenylphosphino)methyl]-3-methylimidazolin-2-ylidene-C,C2 (dppmmi) used as the ancillaiy ligand and 2-phenylpyridine (ppy) and 2-(2,4-difluorophenyl)pyridine (dfppy) used as cyclometalating ligands show much larger photoluminescence quantum yields of 0.24 and 0.46, respectively. ... 

Substitution of cyclometallated 2-phenylpyridine with the more jt-delocaUzed cyclometallated 2-phenylquinoline does not affect significantly the NLO responses, while a lower NLO response is obtained for the Ir NLO chromophore with a cyclometallated 3 -(2-pyridyl)-2,2 5, 2"-terthiophene (ttpy), since the structure of ttpy induces a significant downshift of the HOMO s energy, compared to that of cyclometallated 2-phenylpyridine and 2-phenylquinoline [162]. 

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