Synthesis, Structure, and Photophysical Properties of Mo2(NN)4 and Mo2(NN)2(TiPB)2, Where NN = N,N′-Diphenylphenylpropiolamidinate and TiPB = 2,4,6-Triisopropylbenzoate

Two dimolybdenum compounds featuring amidinate ligands with a C≡C bond, Mo2(NN)4 (I), where NN = N,N′-diphenylphenylpropiolamidinate, and trans-Mo2(NN)2(TiPB)2 (II), where TiPB = 2,4,6-triisopropylbenzoate, have been prepared and structurally characterized by single-crystal X-ray crystallography. Together with Mo2(DAniF)4 (III), where DAniF = N,N′-bis(p-anisyl)formamidinate, all three compounds have been studied with steady-state UV–vis, IR, and time-resolved spectroscopy methods. I and II display intense metal to ligand charge transfer (MLCT). Singlet state (S1) lifetimes of I–III are determined to be 0.7, 19.1, and 2.0 ps, respectively. All three compounds have long-lived triplet state (T1) lifetimes around 100 μs. In femtosecond time-resolved infrared (fs-TRIR) experiments, one ν(C≡C) band is observed at the S1 state for I but two for II, which indicate different patterns of charge distribution. The electron would have to be localized on one NN ligand in I and partially delocalized over two NN ligands ...