Dinuclear and Tetranuclear Gold−Nitrogen Complexes. Solvent Influences on Oxidation and Nuclearity of Gold Guanidinate Derivatives

Abstract

The sodium salt of the Hhpp ligand, Hhpp = 1,3,4,6,7,8-hexahydro-2H-pyrimido[1,2-a]pyrimidine, a 6,6 bicyclic, guanidine system, reacts with (THT)AuCl (THT = tetrahydrothiophene) in THF or CH2Cl2 to form the Au(II) complex, [Au2(hpp)2Cl2]. The Au(II) complex forms either by oxidation with solvents such as CH2Cl2 or disproportionation of Au(I) with concomitant Au(0) formation. The reaction in ethanol gives the colorless tetranuclear Au(I) complex, [Au4(hpp)4]. The tbo ligand, Htbo = 1,4,6-triazabicyclo[3.3.0]oct-4-ene a bicyclic 5,5 guanidine system, behaved differently from the hpp ligand, and only the colorless tetranuclear gold complex, [Au4(tbo)4], formed in THF, CH2Cl2, or ethanol. The X-ray structure of the oxidized species, [Au2(hpp)2Cl2], shows a Au(II)-Au(II) distance of 2.4752(9) A, the shortest gold-gold bond reported prior to the characterization here of the [(PhCOO)6Au4(hpp)2Ag2], Au(II)-Au(II) = 2.4473(19) A. A preliminary description of the formation of this material, obtained by reacting [Au2(hpp)2Cl2] with Ag(OOCPh), is included in this paper. The four Au(I) atoms in the tetranuclear complexes are arranged in a parallelogram with Au-Au distances ranging from 2.8975(5)-2.9392(6) A in [Au4(hpp)4] and 3.1139(12)-3.2220(13) A in [Au4(tbo)4]. density functional theory (DFT) and MP2 calculations on [Au2(hpp)2Cl2] find that the highest occupied molecular orbital (HOMO) is predominately hpp and chlorine-based with some Au-Au delta* character. The lowest unoccupied molecular orbital (LUMO) has metal-to-ligand (M-L) and metal-to-metal (M-M) sigma* character (approximately 50% hpp/chlorine, and 50% gold). DFT calculations on [Au4(hpp)4] show that the HOMO and HOMO-1 are each a mixture of metal-metal antibonding character and metal-ligand antibonding character and that the LUMO is predominately metal based s character (85% Au and 15% hpp).

Transition metal salts dependent intramolecular cyclization of a diimine

“…1. It is shown that N1, C1, C2, N3 and C15 are nearly located in one plane and the N1-C1, C1-C2, C2-N3, N3-C15 and C15-N1 bond lengths and the corresponding bond angles (Table 4) in the ring are comparable to those in the imidazole ring reported [23][24][25][26]. This confirms the existence of the imidazole ring in compound L 2 .…”

Activation of SO2 by N/Si+ and N/B Frustrated Lewis Pairs: Experimental and Theoretical Comparison with CO2 Activation

“…Chem.E ur.J. 2019,25,[8118][8119][8120][8121][8122][8123][8124][8125][8126] www.chemeurj.org tries. Besides, these stabilizing contributionsa re greater for CO 2 adducts (DE = À113.75 kcal mol À1 for TBD-BCy 2 -CO 2 vs. 53.67 kcal mol À1 for TBD-BCy 2 -SO 2 ,T able 5).…”

Synthesis of volatile, reactive coinage metal 5,5-bicyclic amidinates with enhanced thermal stability for chemical vapor deposition

“…The gold atoms and the amidinate N-C-N cores form a single plane, with symmetric Au-N distances of 2.013(3) Å that fall on the short end of typical gold(I) amidinates. 24,30,[34][35][36][37][38][39] The Au···Au distance of 2.855(1) Å is long for a digold(I) amidinate, in which this distance is typically 2.644(2)-2.711(3) Å. 24,30,34,39 The ringconstrained N-C-N angle is also larger than usual, at 131.9(2)° (cf.…”

“…Single-crystal X-ray diffraction confirmed that the gold(I) complex 3 possesses the same solid-state dimeric structure as the copper(I) complex 2 (Figure 1a and Tables S1,2 ,4,6). Gold(I) amidinates and guanidinates typically adopt dimeric 24,30,34 or tetrameric structures, [35][36][37][38] depending on the steric demand of the ligand. One of these tetramers is a gold(I) complex of 1,4,6triazabicyclo[3.3.0]oct-4-ene, 35 the non-methylated guanidine analogue of 1, suggesting that in 3 the four methyl groups per ligand may contribute to the preference for a dimeric structure.…”

“…121.8(5)-128.6(5)° in gold(I) amidinates). 24,30,[34][35][36][37][38][39] Interestingly, molecules of 3 pack face-to-edge (Figures 1b, S7 and Table S6), with three neighboring methyl groups pointing at each planar face of the molecule. A recent review of Au···H-C interactions describes as hydrogen bonding Au I ···H-C distances Au I ···H < 3 Å and Au I ···C < 4 Å, preferably with the Au I ···H -C angle approaching 180°.…”