Platinum Complexes of Alkynyl-Substituted Dimethyldihydropyrenes

Abstract

A series of photochromic dimethyldihydropyrenes (DHP) bearing ethyne substituents in the 4-position ( R DHP-CCH; R = H (4), acetyl (5), benzoyl (6), 1naphthoyl (7), benzo[e] (8)) were prepared for use as precursors to ethynyl ligands. Dehydrohalogenation of the adduct of these ethynes with various PtCl 2 (L) 2 complexes afforded a series of cis and trans square-planar bis(DHPethynyl) platinum complexes, ( R DHP-CC) 2 Pt(L) 2 (cis, R = H, L 2 = PEt 3 (9), acetyl, PEt 3 (10), benzoyl, PEt 3 (11), 1-naphthoyl, PEt 3 (12), benzo[e], PEt 3 (13), benzoyl, PPh 3 (14), benzo[e], PPh 3 (15); trans, R = H, L 2 = dppe (16), benzo[e], dppe (17), acetyl, bipy (18), 1-naphthoyl, bipy (19), H, phen (20)). The DHP-ethynes bearing acyl and benzo[e] substituents on the DHP (5−8) and their platinum complexes (10−19) are photochromic and undergo ring opening to the related cyclophanediene (CPD) isomer on irradiation with visible light (λ >550 nm). In the case of the benzo[e]DHP 8, adding a 4-ethynyl substituent increases the rate of photo-opening 4-fold; however, in the acylDHP series 5−7, addition of a 4-ethynyl group slows the rate of photo-opening by a factor of about 4. The platinum complexes generally open more slowly than the corresponding alkyne precursors, again by a factor of about 4. The rate of photoopening does not appear to be affected significantly by the nature of the ancillary ligands or the metal geometry, suggesting that there is poor electronic communication between the platinum center and the DHP π system. The thermal back-reaction from the open CPD to closed DHP form is about 50% faster for the metal complexes than for the DHP-ethyne precursor. The platinum complexes and the DHP-ethynes were characterized by NMR and IR spectroscopy and MS and by X-ray crystallography for metal complexes 10, 11, 14, 15, and 17.

Tuning the Photoisomerization of a N^C‐Chelate Organoboron Compound with a MetalAcetylide Unit

“…This difference can be explained by the 18 e Re I unit, which takes less electron density away from the pyridyl ring of the N^C chelate compared to the electron‐deficient 14 e Au I unit and the 16 e Pt II unit. The other important feature as revealed from the crystal structure is that, in Pt‐B , the two N^C‐chelate units are coplanar and the π‐conjugation is extended to the two alkyne linkers and the Pt II atom, similar to the observations in some previously reported [ trans ‐Pt(PR 3 ) 2 (acetylide) 2 ] molecules 13b. c In Re‐B , the three carbonyl ligands adopt a facial geometry, which is typical of Re(CO) 3 (bpy)X units,8 to minimize the strong mutual trans effects of the carbonyl groups.…”

Functionalised organometallic photoswitches containing dihydropyrene units

“…23 The limited range of studies regarding these types of complexes requires further structural and electronic characterisation for the design of molecular componetry. [23][24][25] Herein, we describe the synthesis and characterisation of a series of mono-and bimetallic complexes of the type (M(PP) Cp'CuC) n -DHP (M = Ru, Fe; PP = (PPh 3 ) 2 , dppe; Cp′ = Cp, Cp*; n = 1, 2) (Scheme 2). We have investigated their electronic and photochromic properties using electrochemical, and spectroelectrochemical techniques.…”

Light-Gated Modulation of Electronic Mobility of a Dihydropyrene-Based Photochromic Coordination Polymer

“…An excellent member of this class of photochromic system is the 2,7-di- tert -butyl- trans -15,16-dimethyldihydropyrene (DHP)– meta cyclophanediene (CPD) system (Figure A). − Because of the extended π-system, the thermally stable “closed” DHP form is deep green in color with an absorption in the visible region. Upon exposure to visible light, it isomerizes to the colorless, thermodynamically less stable “open-ring” CPD form, where the two out-of-plane phenyl rings are linked by two olefinic bridges. , Therefore, the π-conjugation of a 14π aromatic DHP photoisomerizes to two discrete 6π electronic phenyl rings in the CPD form (Figure A). The less conjugated CPD isomer reverts to the highly conjugated DHP isomer under the exposure to UV irradiation or heating.…”

“…Upon exposure to visible light, it isomerizes to the colorless, thermodynamically less stable "open-ring" CPD form, where the two out-of-plane phenyl rings are linked by two olefinic bridges. 21,22 Therefore, the π-conjugation of a 14π aromatic DHP photoisomerizes to two discrete 6π electronic phenyl rings in the CPD form (Figure 1A). The less conjugated CPD isomer reverts to the highly conjugated DHP isomer under the exposure to UV irradiation or heating.…”