Optical spectroscopic studies of light-harvesting by pigment-reconstituted peridinin-chlorophyll-proteins at cryogenic temperatures

Low temperature, steady-state, optical spectroscopic methods were used to study the spectral features of peridinin-chlorophyll-protein (PCP) complexes in which recombinant apoprotein has been refolded in the presence of peridinin and either chlorophyll a (Chl a), chlorophyll b (Chl b), chlorophyll d (Chl d), 3-acetyl-chlorophyll a (3-acetyl-Chl a) or bacteriochlorophyll a (BChl a). Absorption spectra taken at 10 K provide better resolution of the spectroscopic bands than seen at room temperature and reveal specific pigment–protein interactions responsible for the positions of the Q(y) bands of the chlorophylls. The study reveals that the functional groups attached to Ring I of the two protein-bound chlorophylls modulate the Q(y) and Soret transition energies. Fluorescence excitation spectra were used to compute energy transfer efficiencies of the various complexes at room temperature and these were correlated with previously reported ultrafast, time-resolved optical spectroscopic dynamics data. The results illustrate the robust nature and value of the PCP complex, which maintains a high efficiency of antenna function even in the presence of non-native chlorophyll species, as an effective tool for elucidating the molecular details of photosynthetic light-harvesting

Synthesis and Structure of Platinum Bis(phospholane) Complexes Pt(diphos*)(R)(X), Catalyst Precursors for Asymmetric Phosphine Alkylation

The complexes Pt­((<i>R,R</i>)-Me-DuPhos)­(Ph)­(Cl) (<b>1</b>) and Pt­((<i>R,R</i>)-<i>i</i>-Pr-DuPhos)­(Ph)­(Cl) (<b>2</b>) have been used as catalyst precursors in Pt-catalyzed asymmetric alkylation of secondary phosphines. To investigate structure–reactivity–selectivity relationships in these reactions, analogous complexes with different bis­(phospholane) ligands and/or Pt-hydrocarbyl groups were prepared. Treatment of Pt­(COD)­(R)­(Cl) (R = Me, Ph) with BPE or DuPhos ligands gave Pt­((<i>R,R</i>)-Me-BPE)­(Me)­(Cl) (<b>3</b>), Pt­((<i>R,R</i>)-Ph-BPE)­(Me)­(Cl) (<b>5</b>), Pt­((<i>R,R</i>)-Ph-BPE)­(Ph)­(Cl) (<b>6</b>), and Pt­((<i>R,R</i>)-<i>i</i>-Pr-DuPhos)­(Me)­(Cl) (<b>7</b>). However, treatment of Pt­(COD)­(Me)­(Cl) with (<i>R,R</i>)-Me-FerroLANE gave a mixture of products, which were converted upon heating to Pt­((<i>R,R</i>)-Me-FerroLANE)­(Me)­(Cl) (<b>8</b>). A related mixture formed from Pt­(COD)­(Ph)­(Cl) precipitated <i>trans</i>-[Pt­((<i>R,R</i>)-Me-FerroLANE)­(Ph)­(Cl)]_<i>n</i> (<b>9T</b>), which on treatment with AgOTf followed by LiCl gave <i>cis</i>-Pt­((<i>R,R</i>)-Me-FerroLANE)­(Ph)­(Cl) (<b>9</b>) as the major product. The reaction of Pt­(COD)­(Ph)­(Cl) with (<i>R,R</i>)-Me-BPE gave the dinuclear dication [(Pt­((<i>R,R</i>)-Me-BPE)­(Ph))₂(μ-(<i>R,R</i>)-Me-BPE))]­[Cl]₂ (<b>10</b>) instead of the expected Pt­((<i>R,R</i>)-Me-BPE)­(Ph)­(Cl) (<b>4</b>). The iodide Pt­((<i>R,R</i>)-Me-BPE)­(Ph)­(I) (<b>11</b>) was formed from Pt­(COD)­(Ph)­(I) and BPE but decomposed readily. Treatment of Pt­(COD)­X₂ with (<i>R,R</i>)-Me-BPE gave Pt­((<i>R,R</i>)-Me-BPE)­X₂ (X = Cl (<b>12</b>), I (<b>13</b>)). Reaction of Pt­(COD)­Ph₂ with (<i>R,R</i>)-Me-BPE gave Pt­((<i>R,R</i>)-Me-BPE)­Ph₂ (<b>14</b>), which was protonated with HCl to yield <b>4</b>. Treatment of Pt­((<i>R,R</i>)-Me-DuPhos)­Cl₂ with excess (9-phenanthryl)magnesium bromide gave Pt­((<i>R,R</i>)-Me-DuPhos)­(9-phenanthryl)­(Br) (<b>15</b>), while a similar reaction with excess (6-methoxy-2-naphthyl)­magnesium bromide gave Pt­((<i>R,R</i>)-Me-DuPhos)­Ar₂ (<b>16</b>). Complexes <b>3</b>, <b>4</b>, <b>6</b>–<b>10</b>, and <b>12</b>–<b>14</b> were structurally characterized by X-ray crystallography. Structure–reactivity–selectivity relationships in this series of Pt catalyst precursors were investigated in the catalytic alkylation of the bis­(secondary phosphine) PhHP­(CH₂)₃PHPh with benzyl bromide

Synthesis, Structure, Dynamics, and Selective Methylation of Platinum and Palladium Diphosphametallacyclobutane Complexes

Treatment of M­(dppe)­Cl₂ (M = Pd, Pt) or Pt­((<i>R,R</i>)-Me-DuPhos)­Cl₂ with IsHPCH₂PHIs (<b>1</b>; Is = isityl = 2,4,6-(<i>i</i>-Pr)₃C₆H₂) and 2 equiv of NaOSiMe₃ gave the mononuclear diphosphametallacyclobutane complexes M­(dppe)­(IsPCH₂PIs) (M = Pd (<b>2</b>), Pt (<b>3</b>)), or Pt­((<i>R,R</i>)-Me-DuPhos)­(IsPCH₂PIs) (<b>4</b>). Dynamic processes involving phosphorus inversion and rotation about the P–C­(Is) bonds in <b>2</b>–<b>4</b> were characterized by variable-temperature NMR spectroscopy, which suggested that each existed as a single <i>C</i>₂-symmetric diastereomer in solution, consistent with their solid-state structures determined by X-ray crystallography. The MiniPhos derivative IsMePCH₂PMeIs (<b>5</b>) was prepared as a 5.5/1 <i>rac</i>/<i>meso</i> mixture by sequential arylation and methylation of Cl₂PCH₂PCl₂. Alternatively, the catalyst precursor Pt­((<i>R,R</i>)-Me-DuPhos)­(Ph)­(Cl) mediated alkylation of secondary phosphines in the presence of NaOSiMe₃ to yield selectively <i>meso</i>-<b>5</b> either from PHMe­(Is) and CH₂I₂ or from <b>1</b> and MeI. Recrystallization and chromatography yielded diastereomerically enriched <i>rac</i>-<b>5</b> and <i>meso</i>-<b>5</b>. Treatment of M­(dppe)­(OTf)₂ (M = Pd, Pt) or Pt­((<i>R,R</i>)-Me-DuPhos)­(OTf)₂ with <i>meso</i>-<b>5</b> gave the dications <i>meso</i>-[M­(diphos)­(IsMePCH₂PMeIs)]­[OTf]₂ (M­(diphos) = Pd­(dppe) (<b>6</b>), Pt­(dppe) (<b>8</b>), Pt­((<i>R,R</i>)-Me-DuPhos) (<b>10</b>)). Similar reactions of <i>rac</i>-<b>5</b> yielded the dications <i>rac</i>-[M­(diphos)­(IsMePCH₂PMeIs)]­[OTf]₂ (M­(diphos) = Pd­(dppe) (<b>7</b>), Pt­(dppe) (<b>9</b>)) and a 1/1 mixture of the <i>C</i>₂-symmetric diastereomers [Pt­((<i>R,R</i>)-Me-DuPhos)­(IsMePCH₂PMeIs)]­[OTf]₂ (<b>11a</b>,<b>b</b>). Treatment of <b>2</b> and <b>3</b> with 2 equiv of methyl triflate gave the dications <b>6</b>–<b>9</b> as ca. 1/1 <i>meso</i>/<i>rac</i> mixtures, and methylation of <b>4</b> selectively gave one of the <i>C</i>₂-symmetric diastereomers, <b>11a</b>. These alkylations proceeded via the observable monomethylated intermediates [M­(diphos)­(IsMePCH₂PIs)]­[OTf] (<b>12</b>–<b>14</b>)

Synthesis, Structure, Dynamics, and Selective Methylation of Platinum and Palladium Diphosphametallacyclobutane Complexes

Treatment of M­(dppe)­Cl₂ (M = Pd, Pt) or Pt­((<i>R,R</i>)-Me-DuPhos)­Cl₂ with IsHPCH₂PHIs (<b>1</b>; Is = isityl = 2,4,6-(<i>i</i>-Pr)₃C₆H₂) and 2 equiv of NaOSiMe₃ gave the mononuclear diphosphametallacyclobutane complexes M­(dppe)­(IsPCH₂PIs) (M = Pd (<b>2</b>), Pt (<b>3</b>)), or Pt­((<i>R,R</i>)-Me-DuPhos)­(IsPCH₂PIs) (<b>4</b>). Dynamic processes involving phosphorus inversion and rotation about the P–C­(Is) bonds in <b>2</b>–<b>4</b> were characterized by variable-temperature NMR spectroscopy, which suggested that each existed as a single <i>C</i>₂-symmetric diastereomer in solution, consistent with their solid-state structures determined by X-ray crystallography. The MiniPhos derivative IsMePCH₂PMeIs (<b>5</b>) was prepared as a 5.5/1 <i>rac</i>/<i>meso</i> mixture by sequential arylation and methylation of Cl₂PCH₂PCl₂. Alternatively, the catalyst precursor Pt­((<i>R,R</i>)-Me-DuPhos)­(Ph)­(Cl) mediated alkylation of secondary phosphines in the presence of NaOSiMe₃ to yield selectively <i>meso</i>-<b>5</b> either from PHMe­(Is) and CH₂I₂ or from <b>1</b> and MeI. Recrystallization and chromatography yielded diastereomerically enriched <i>rac</i>-<b>5</b> and <i>meso</i>-<b>5</b>. Treatment of M­(dppe)­(OTf)₂ (M = Pd, Pt) or Pt­((<i>R,R</i>)-Me-DuPhos)­(OTf)₂ with <i>meso</i>-<b>5</b> gave the dications <i>meso</i>-[M­(diphos)­(IsMePCH₂PMeIs)]­[OTf]₂ (M­(diphos) = Pd­(dppe) (<b>6</b>), Pt­(dppe) (<b>8</b>), Pt­((<i>R,R</i>)-Me-DuPhos) (<b>10</b>)). Similar reactions of <i>rac</i>-<b>5</b> yielded the dications <i>rac</i>-[M­(diphos)­(IsMePCH₂PMeIs)]­[OTf]₂ (M­(diphos) = Pd­(dppe) (<b>7</b>), Pt­(dppe) (<b>9</b>)) and a 1/1 mixture of the <i>C</i>₂-symmetric diastereomers [Pt­((<i>R,R</i>)-Me-DuPhos)­(IsMePCH₂PMeIs)]­[OTf]₂ (<b>11a</b>,<b>b</b>). Treatment of <b>2</b> and <b>3</b> with 2 equiv of methyl triflate gave the dications <b>6</b>–<b>9</b> as ca. 1/1 <i>meso</i>/<i>rac</i> mixtures, and methylation of <b>4</b> selectively gave one of the <i>C</i>₂-symmetric diastereomers, <b>11a</b>. These alkylations proceeded via the observable monomethylated intermediates [M­(diphos)­(IsMePCH₂PIs)]­[OTf] (<b>12</b>–<b>14</b>)