Crystallographic and Spectroscopic Characterization of Tetrakis(μ-N,N′-diarylformamidinato)dichlorodirhenium(III,III) Compounds

Abstract

Through a variation in the aryl substituents of the formamidinate ligand, a variety of dirhenium compounds has been synthesized with [XArNC(H)NArX]− where Ar is a substituted C6H5 or C6H4 aryl ring and × is p‐MeO (1), H (3), m‐MeO (4), p‐Cl (5), m‐Cl (6), m‐CF3 (7), p‐CF3 (8), 3,4‐Cl2 (9), and 3,5‐Cl2 (10a, 10b). UV/Vis and NMR spectroscopy and electrochemical data for 1and 3–10 have been obtained. X‐ray crystallographic analysis of Re2Cl2(μ‐form)4 with four different diarylformamidinate ligands and one analog with two different interstitial solvents are presented; Re2Cl2[(p‐MeOC6H4)NCHN(p‐MeOC6H4)]4 (1), Re2Cl2[(m‐MeOC6H4)‐NCHN(m‐MeOC6H4)]4 · 2 CH2Cl2 (4), Re2Cl2[(3,4‐Cl2C6H3)NCHN(3,4‐Cl2C6H3)]4 · 2 CH2Cl2 (9), Re2Cl2[(3,5‐Cl2C6H3)NCHN(3,5‐Cl2C6H3)]4 · 4 CH2Cl2 (10a), and Re2Cl2[(3,5‐Cl2C6H3)NCHN(3,5‐Cl2C6H3)]4 · OC4H8 (10b).

Direct Observation of the Luminescence from the 3δδ* Excited State of Re2Cl2(p-OCH3form)4

“…22,29,30 The greater energy difference expected between the 3 δδ* excited state and the 1 δ 2 ground state in these systems led us to explore the 3 δδ* luminescence from Re 2 Cl 2 (p-OCH 3 form) 4 (p-OCH 3 form ) p-methoxy-formamidinate), whose structure is shown in Figure 1b. 31 The room temperature electronic absorption, emission (λ ex ) 420 nm), and excitation (λ em ) 800 nm) spectra of Re 2 -Cl 2 (p-OCH 3 form) 4 in CH 3 CN and CH 2 Cl 2 are shown in Figure 2, along with the emission spectrum of the solid (λ ex ) 420 nm) collected at 77 K. 32 The absorption spectra are consistent with those previously reported for dirhenium-(III,III) tetra-formamidinates, 29 possessing maxima at 414, 413, and 438 nm in CH 2 Cl 2 , THF, and CH 3 CN, respectively, with ∼ 12 000 M -1 cm -1 . This peak was previously assigned to the 1 δ 2 f 1 δδ* ( 1 A 1g f 1 A 2u ) transition.…”

“…This assignment is also supported by the shift of this peak to higher for Re 2 Cl 2 (p-Cl-form) 4 (λ max ) 400 nm, CH 2 Cl 2 ), for which the formamidinate ligand is harder to oxidize. 31 Similarly, a shift in the absorption maximum from 409 nm for Re 2 Cl 2 (m-OCH 3 form) 4 to 392 nm for Re 2 Cl 2 (m-Cl-form) 4 is observed in CH 2 Cl 2 , 31 which also correlates with the ease of ligand oxidation. In all complexes, a shoulder is observed at ∼465 nm ( ∼4000 M -1 cm -1 ), whose position is invariant to solvent or the substituent on the formamidinate.…”

Nitrile Hydrolysis Promoted by Rhenium(III) Metal-Metal Bonded Systems

“…In comparison to the parent compound [N(C 4 H 9 ) 4 ] 2 [Re 2 Cl 8 ] with a d to d * transition between 680 -690 nm depending on the solvent, [97] [59] and [N(C 4 H 9 ) 4 ] 2 [Re 4 Cl 12 (m-1,4-(C(O) NH) 2 C 6 H 4 )] (666 nm) [60] is observed at higher energy. The trend to higher energy is to be expected since the d to d * transition for the formamidinate and carboxylate complexes Re 2 Cl 2 (m-form) 4 , Re 2 Cl 4 (m-O 2 CR) 2 , and Re 2 Cl 2 (m-O 2 CR) 4 fall in the general ranges of 386 -418 nm, [98] 633 -635 nm, [99] and 495 -560 nm, [100] respectively.…”

Expanding the Chemistry of Rhenium Metal–Metal Bonded Fluoro Complexes: Facile Preparation and Characterization of Paddlewheel Complexes

“…Selected bond distances and angles are given in Tables and . There are no chloro and bromo analogues of 2 ; the structural parameters were compared with those in Re 2 (ArNCHNAr) 4 Cl 2 (where Ar = CH 3 C 6 H 5 (2.2759(3) Å), p -OMe (2.2777(3) Å), m -OMe (2.2765(6) Å), 3,4-Cl 2 (2.2783(4) Å), 3,5-Cl 2 , (2.2734(3) Å)) . In 2 , the Re–Re′ bond distance (2.2575(2) Å) is ∼0.02 Å shorter than in Re 2 (ArNCHNAr) 4 Cl 2 (Ar = CH 3 C 6 H 5 (2.2759(3) Å), p -OMe (2.2777(3) Å), m -OMe (2.2765(6) Å), 3,4-Cl 2 (2.2783(4) Å), 3,5-Cl 2 (2.2734(3) Å)) …”