Tuning the Excited-State Properties of Luminescent Rhenium(V) Benzylidyne Complexes Containing Phosphorus and Nitrogen Donor Ligands

Abstract

Efficient methods are developed for the synthesis of rhenium(V)-substituted benzylidyne complexes with various auxiliary ligands to facilitate the tuning of their excited-state properties. The electronic structures and spectroscopic and photophysical properties of [Re(⋮CAr‘)(pdpp)2Cl]+ (Ar‘ = C6H2Me3-2,4,6, pdpp = o-phenylenebis(diphenylphosphine), 2), [Re(⋮CAr‘)L2(CO)(H2O)Cl]+ (L = PPh3, 3; P(C6H4OMe-p)3, 4; PPh2Me, 5), [Re(⋮CAr‘)(dppe)(CO)2Cl]+ (dppe = 1,2-bis(diphenylphosphino)ethane, 6), [Re(⋮CAr‘)(L−L)(CO)2Cl]+ (L−L = 2,2‘-bipyridine, 7; 4,4‘-dichloro-2,2‘-bipyridine, 8; 4,4‘-dimethoxycarbonyl-2,2‘-bipyridine, 9), [Re(⋮CAr‘)(Tp‘)(CO)2]+ (Tp‘ = tris(3,5-dimethyl-1-pyrazolyl)borohydride, 10), and [Re(⋮CC6H4-R)(pdpp)(CO)2(O3SCF3)]+ (13, R = OMe, a; Me, b; H, c; Cl, d; Br, e; CN, f) are studied and compared. The molecular structures of 7·CHCl3 , 10, 12f, 13a·CH3OH·H2O, and 13d·2CH2Cl2 are determined by X-ray crystallography and reveal Re⋮C distances in the 1.766(8)−1.786(7) Å range. HF-SCF calculations on the model compounds [Re(⋮CC6H5)(H2PCHCHPH2)2Cl]+ (2m), [Re(⋮CC6H5)(PH3)2(H2O)(CO)Cl]+ (3m), and [Re(⋮CC6H5)(H2PCHCHPH2)(CO)2(OH)]+ (13m) suggest that the HOMO is π(Re⋮C−Ph) and the LUMO is π*(Re⋮C−Ph). CI-singles calculations on the excited state of optimized 2m indicate that the lowest energy UV−vis absorption of 2 − 6, 10, and 13 originates from a HOMO to LUMO spin-forbidden transition. This is identified as 3[π(Re⋮CAr) → π*(Re⋮CAr)], where d(Re) → p(⋮C) MLCT character is apparent and the p(⋮C) orbital and phenyl π system are conjugated. The UV−vis absorption spectra of 7 − 9 are significantly different, and their lowest energy absorption is assigned d(Re) → π*(X2-bpy). The rhenium(V) benzylidyne complexes are highly emissive at room temperature and 77 K. The combination of spectroscopic studies and theoretical calculations suggest that the emitting state of 2 − 6, 10, and 13 is 3[π(Re⋮CAr)→π*(Re⋮CAr)] but that of 7 − 9 is d(Re) → π*(X2-bpy). The emission energies in dichloromethane can be adjusted from 520 to 610 nm by variation of the benzylidyne and ancillary ligands. Their electrochemical behaviors are examined and provide further evidence to support the excited-state assignment.

Alkyne Metathesis Reactions of Rhenium(V) Carbyne Complexes

“…The complex 12 is the first example of rhenium arylcarbyne complexes obtained by alkyne metathesis. Previously reported rhenium arylcarbyne complexes are usually obtained by electrophilic abstraction of aryl alkoxycarbene or acyl , complexes and dehydrogenation of methyl groups of toluene derivatives with electron-rich rhenium complexes. , For example, [CpRe­(CPh)­(CO) 2 ]­BCl 4 was synthesized by the reaction of CpRe­{C­(OMe)­Ph}­(CO) 2 with BCl 3 , [Re­(OTf)­{C­(2,4,6-C 6 H 2 Me 3 )}­(CO) 4 ]­OTf was prepared by the reaction of Re­{C­(O)­(2,4,6-C 6 H 2 Me 3 )}­(CO) 5 with (CF 3 SO 2 )­O, and ReH­(CPh)­(PNP) (PNP = ( i Pr 2 PCH 2 SiMe 2 ) 2 N) was obtained by the reaction of PhCH 3 with (PNP)­ReH 4 or (PNP)­ReH 2 (η 2 -cyclooctyne) …”

Synthesis of Rhenium Vinylidene and Carbyne Complexes from Reactions of [Re(dppm)3]I with Terminal Alkynes and Alkynols

“…This work reported here stems from our effort in the development of synthetic methods for carbonyl-free d 2 rhenium­(V) vinylcarbyne complexes. To the best of our knowledge, rhenium vinylcarbyne complexes reported prior to our work are limited to the carbonyl-containing complexes [Re­(CC­(R)CPh 2 )­(CO) 2 (triphos)]­(OTf) 2 (R = H, Me) and [Cp*­(CO) 2 (CCHCMe 2 )]­BF 4 , although a number of d 2 Re­(V) carbyne complexes are now known. − …”

“…The one-pot reactions of 1 with alkynes and alkynols to give carbyne complexes [ReI­(CCH 2 R)­(dppm) 2 ]I ( 9 ) and vinylcarbyne complexes [ReI­(CCHCRR′)­(dppm) 2 ]I ( 10 ) are interesting, as they provide a convenient way to obtain carbonyl-free rhenium­(V) carbyne complexes, which are potentially useful in materials chemistry and organometallic synthesis. Although many d 2 Re­(V) carbyne complexes containing one or more carbonyl ligands have been reported, − , d 2 Re­(V) carbyne complexes without a CO ligand are less known. The complexes {R′ 2 PCH 2 SiMe 2 ) 2 N}­HReCR (R′ = Cy, i Pr) were prepared from the reactions of {R′ 2 PCH 2 SiMe 2 ) 2 N}­ReH 4 with alkenes or alkanes .…”

Luminescent metal complexes derived from carbene and related ligands: tuning excited-state properties with metal–carbon multiple bonds

“…Significantly, these photophysical responses are reversible upon treat-namely (i) 2,4,6-trimethylbenzylidyne species bearing various phosphorus or nitrogen donor ligands (D), and (ii) para-substituted benzylidyne derivatives supported by o-phenylenebis(diphenylphosphine) (E, Fig. 7), have been developed [10,11]. The rhenium(V) benzylidyne complexes display photoluminescence at room temperature and 77 K. Data from electronic absorption and emission spectra, electrochemistry, and molecular orbital calculations provided evidence to suggest that the excited state for diimine-supported species is d(Re) p*(X 2 -bpy).…”

“…The first observation of a metal p*(carbene) charge transfer excited state in solution at ambient temperatures was reported by our group for the hexanuclear platinum(II) macrocycle [Pt(CN)-(C 10 H 21 N 4 )] 6 bearing chelating bis(carbene) and bridging cyanide ligands [7]. Our endeavors in developing luminescent metal-carbon multiple-bonded species have also proved fruitful for low-valent Pt(II) [8] and Re(I) [9] carbene derivatives supported by diimine auxiliaries, while the preparation and excited-state properties of high-valent Re(V) [10,11] and -(VI) [12] alkylidyne luminophores have been undertaken; an overview of this body of work is given at the end of this account. Mayr et al [13] first noted fluid luminescence from alkylidyne complexes in 1985, but reports of further examples remain sparse [14,15].…”