New nonlinear optical (NLO) materials are essential to the development of optoelectronic technologies, such as optical communications, high-speed electrooptical information processing, short optical-pulse generation, and all-optical switching. [1] For practical NLO devices, such as optical limiting devices, only a few appropriate nonlinear materials are currently available. This has been a primary barrier to the development of these optical devices, which can control the amplitude, phase, polarization, or direction of optical beams. [2±4] Among the large number of NLO absorbers that have been identified, metallophthalocyanines and related compounds have emerged as the most promising materials owing to their large nonlinearities (originating from optical pumping of lowlying electronic states), ultrafast response times, and easy processability. [2, 4] [tBu 4 PcInCl] (Pc ¼ phthalocyanine) has been used to prepare optical limiters, [4] which can reduce optical damage to elements that are sensitive to sudden highintensity light, such as sensors or human eyes. The effect of axial substitution on the optical properties of indium(iii) phthalocyanines was studied systematically in our research group, and by Shirk and co-workers. [3] The optical-limiting properties of the axially substituted indium phthalocyanine monomers were surprisingly robust to structural changes in the axial position. [3] Dimers, in comparison with monomeric phthalocyanines (Pcs), may show increased third-order nonlinearities as a result of intramolecular p±p interactions of the Pc units. Additionally, the optical-limiting properties of these compounds are influenced by the dimeric structure. In this regard, we report here for the first time an axially linked indium phthalocyanine dimer with a direct InÀIn bond.Organometallic compounds containing metal±metal single bonds between the metallic elements of Group 3A (Al, Ga, In, and Tl) are quite unusual, [5a] but also of great interest in materials science. [5] So far, only metallophthalocyanine dimers with transition-metal±transition-metal bonds, for example, Ru¼Ru, [6,7] Os¼Os, [8] MoÀMo, [9] RhÀRh, [10] IrÀIr, [11] and Re Re [12] are known. Kobayashi et al claimed to have prepared (PcSiX) 2 with a direct Si À Si bonding interaction [13a] but this has since been proved to be incorrect. [13b] Very recently, however, the same research group have again reported to have obtained Pc dimers linked by an SiÀSi bond. [13c] We attempted to prepare a dimeric indium phthalocyanine complex with an InÀIn bond, by the reaction of soluble [tBu 4 PcInCl] (1) [3a] with activated magnesium turnings in freshly dried THF in the presence of a catalytic amount of iodine, but all efforts were unsuccessful. Further investigations showed that the pure dimer [tBu 4 PcInÀInPctBu 4 ], that is, without an associated N donor ligand, is unstable in solution under the classical Wurtz coupling conditions. These findings are in agreement with the observations of Tuck and coworkers, [14] who successfully prepared stable N...
