Article Cite This: Inorg. Chem. XXXX, XXX, XXX−XXX
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Unusual Water-Soluble Imino Phosphine Ligand: Enamine and Imine Derivatives of 1,3,5-Triaza-7-phosphaadamantane (PTA) Raphel A. E. Enow, Wei-Chih Lee, Travis D. Cournoyer, Travis L. Sunderland, and Brian J. Frost* Department of Chemistry, University of Nevada, Reno, Nevada 89557-0216, United States
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S Supporting Information *
ABSTRACT: A series of water-soluble and air-stable Eenamine derivatives of 1,3,5-triaza-7-phosphaadamantane (PTA), PTAC(R)NH2, 1−4, are reported along with data on E−Z isomerization and tautomerization to the imine form (PTA-CRNH). Reaction of 1,3,5-triaza-7-phosphaamantane-6-yl lithium, PTA-Li, with aromatic nitriles afforded Eenamine derivatives of PTA in good yield (49−91%). Phosphines 1−4 are stable toward water and air, and do not appear to isomerize or tautomerize, unless coordinated to a metal or oxidized. The corresponding oxides, OPTA C(R)NH2 (5−8), were observed as ∼55/45 mixtures of E and Z isomers. Kinetic data on the E−Z isomerization is reported. Upon coordination of 1−4 to W(CO)4(pip)2, a κ1-P enamine is formed, [W(CO)4(pip)(κ1-P-PTACRNH2)]. Enamine− imine tautomerization of the metal bound phosphine was observed resulting in κ2-P,N imine complexes, [W(CO)4(κ2-P,NPTA-CRNH)], 9−12. The crystal structures of the κ1-P enamine 11a, κ2-P,N imine 9 and 12, phosphines 1 and 3, as well as phosphine oxide 8a were obtained. DFT calculations on the various isomers of the phosphines and phosphine oxides are also reported.
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INTRODUCTION Our research group has had a long-standing interest in P,N ligands and specifically the chemistry of 1,3,5-triaza-7phosphaadamantane (PTA), a small, neutral, air-stable, and water-soluble phosphine that has been utilized to enhance the water solubility of metal complexes, in catalysis, and in medicine.1−3 We have been attracted to the coordination chemistry of PTA,4−10 the use of PTA as a ligand in catalysis,11−16 and the synthesis of water-soluble derivatives of PTA.17−21 In particular we, and others, have developed a methodology for modification of the “upper rim” of the phosphine, which may be accomplished via deprotonation of an α-methylene adjacent to phosphorus and insertion of an electrophile. “Upper rim” PTA derivatives have been reported via insertion of electrophiles such as chlorophosphines (ClPR2),17,21 CO2,19 aryl ketones,19,22 aryl aldehydes,19,22−24 and imines20 into the C−Li bond of lithiated PTA (PTA-Li) (Scheme 1).25 Recently, we became interested in chelating and hemilabile ligands containing P,N donor groups.14,20 To this end we reported a series of β-amino phosphine derivatives of PTA which exhibit hemilabile character and improved catalytic efficiency for nitrile hydration relative to the parent ligand PTA.20 Chelating and hemilabile P,N ligands are important in transition metal catalysis.26−30 The mixture of the soft P donor with the harder N donor, the latter can often serve as a hemilabile ligand, has proven useful.28,30 Imino phosphine ligands on the other hand provide a soft P donor and, in general, a stronger bonding, slightly softer imine donor capable © XXXX American Chemical Society
Scheme 1
of π-accepting. Imino phosphine type ligands have been most commonly based on oxazoline,27,28 ferrocene,31,32 pyridine,30,33,34 or a more general R′2P(CR2)nCNR framework (n = 0−3).26,35−37 In most cases the substituent on the imine nitrogen is something other than hydrogen. Crochet et al. reported significant differences in reactivity between amino phosphines and imino phosphines in the hydrogenation of ketones.38 Received: April 27, 2018
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DOI: 10.1021/acs.inorgchem.8b01167 Inorg. Chem. XXXX, XXX, XXX−XXX
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Inorganic Chemistry
enamine derivatives of PTA are significantly less soluble than the parent PTA (235 g/L; 1.5 M) or the previously reported derivatives PTA-CO2Li, PTA-CH(1-MeIm)(OH), and PTAC(1-MeIm)2(OH).19,22 Enamines 1−4 were characterized by 1H, 13C{1H}, and 31 1 P{ H} NMR spectroscopies as well as IR spectroscopy, GC− MS, HR-MS, and single crystal X-ray analysis. The 31P{1H} NMR spectra of 1−4 contain a single resonance at −87.1, −87.3, −86.8, and −87.9 ppm, respectively. These chemical shifts are upfield of the β-aminophosphines and β-phosphino alcohols previously reported (Table 1) and are comparable to the phosphorus chemical shifts reported for PTA-CO2Li (−88 ppm) and PTA-CO2Me (−93 ppm).19 The 1H and 13C{1H} NMR spectra for the PTA region of 1−4 are less complicated than many of the previously reported “upper rim” PTA derivatives due to the approximate Cs symmetry of 1−4 versus C1 symmetry for many of the other derivatives. The six NCH2N protons are observed between 4.82 and 4.46 ppm in the 1H NMR spectrum, and the four “upper rim” PCH2N methylene protons appear between 3.75 and 3.91 ppm consistent with previously reported values. A broad singlet integrating as two protons is observed for each compound between 4.33 and 4.37 ppm and has been assigned as the NH2. This assignment is confirmed by addition of D2O resulting in a loss of the NMR signal for the amine due to H/D exchange. The 13C{1H} NMR spectrum for the “upper rim” carbons of 1 appears as doublets at 52.8 ppm (2 carbons, 1JPC = 17.7 Hz) and 149.6 ppm (1 carbon, 1JPC = 33.6 Hz). The resonance at 149.6 ppm is shifted significantly from the parent PTA and is consistent with an sp2 carbon center. Two of the “lower rim” NCH2N carbons in 1 are equivalent and appear as a doublet at 74.8 ppm (3JPC = 1.7 Hz). The remaining NCH2N carbon appears as a doublet at 73.9 ppm (3JPC value of 2.8 Hz). The β-carbon, the carbon directly connected to the PTA cage, resonates at 115.7 ppm (2JPC = 12.9 Hz) in 1. Enamines 2−4 have chemical shifts, and coupling constants are similar to that for 1 (see Experimental Section or Supporting Information for additional details). Solid state IR spectroscopy was performed on compounds 1−4 with the symmetric ν(NH) observed between 3280 and 3377 cm−1 and the asymmetric ν(NH) observed between 3309 and 3372 cm−1. Consistent with a Hooke’s law calculation for NH vs ND, the ν(NH) shifts ∼900
Herein we continue our work on the development of novel air-stable and water-soluble phosphine ligands with an emphasis on those with the ability to bind in a bidentate manner. We report here the reaction of aromatic nitriles with PTA-Li leading to β-phosphino-enamines, potential κ2-P,Nderivatives of PTA with an sp2-carbon on the PTA cage. The imino phosphine ligands reported in this work are unusual due the presence of hydrogen as the substituent on the imino nitrogen.
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RESULTS AND DISCUSSION A series of enamine derivatives of PTA (PTACRNH2, 1−4) were synthesized by reaction of PTA-Li with aromatic nitriles followed by aqueous workup (Scheme 2). The imine tautomer Scheme 2
(PTA-CRNH) was not observed (vide inf ra) but is presumed to be a reaction intermediate. Phosphines 1−4 were isolated in modest to excellent yield (49−91%) as white solids and represent the first reported PTA derivatives with an sp2-carbon atom in the PTA cage. The byproducts, PTA and LiOH, were removed by washing with cold water, and unreacted nitrile was removed by washing with diethyl ether. Enamines 1−4 are soluble in common organic solvents such as tetrahydrofuran, dichloromethane, chloroform, methanol, and ethanol, and insoluble in hexane, pentane, and diethyl ether. The water solubility of 1−4 ranges from 3.7 to 4.7 g/L (Table 1): 4.0 g/L (15 mM) for 1, 4.2 g/L (18 mM) for 2, 3.7 g/L (13 mM) for 3, and 4.7 g/L (13 mM) for 4. These values are similar to those for the previously reported β-aminophosphines derivatives of PTA (2−5 g/mL, 7−14 mM)20 and reflect less solubility than those of the previously reported β-phosphinoalcohol derivatives (5−12 g/L; 18−37 mM).19,23 The Table 1.
31
P{1H} NMR Spectroscopic Data and Water Solubility Data for Various PTA Derivatives compd 39
PTA PTA-CO2Li19 PTA-CH(1MeIm)OH22 PTA-C(1MeIm)2OH22 PTA-C(p-C6H4OMe)2OH19 PTA-CH(p-C6H4NMe2)OH23 PTA-CPh2OH19 PTA-CH(p-C6H4OMe)OH19 PTA-CHPhNHPh20 PTA-CH(p-C6H4OCH3)NHPh20 PTA-CPh2NHPh20 PTAC(C6H5)NH2, 1 PTAC(C6H4Me)NH2, 2 PTAC(p-C6H4OMe)NH2, 3 PTAC(C6H2(OMe)3)NH2, 4
31
P{1H} NMR
−98.3a −88.0a −103.4, −104.7b −97.6c −96.4b −102.7, −106.3b −95.5b −102.6, −105.7b −102.4, −105.9b −102.1, −105.9b −97.7b −87.1b −87.3b −86.8b −87.9b
M (mol/L)
S20° (g/L)
1.50 3.86 1.20 0.225 0.027 0.006 0.018 0.038 0.014 0.013 0.007 0.015 0.018 0.013 0.013
235 ∼800 320 78 10.6 1.9 5.9 11.1 4.8 4.9 2.7 4.0 4.2 3.7 4.7
a
D2O. bCDCl3. cCD2Cl2. B
DOI: 10.1021/acs.inorgchem.8b01167 Inorg. Chem. XXXX, XXX, XXX−XXX
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Inorganic Chemistry cm−1 to between 2372 and 2598 cm−1 upon exchange with D2O. X-ray quality crystals were grown by slow evaporation of 1:1 solutions of dichloromethane/hexane containing 1, 3, or 4. The solid state structures of 1 (Figure 1), 3 (Figure 2), and 8a
(Figure 3, 4 oxidized during crystal growth) were determined by X-ray crystallography. All three structures were found as the
Figure 3. Thermal ellipsoid representation (50% probability) of O PTACNH2 (C6H2(OMe)3), 8a, with the atomic numbering scheme. Hydrogen atoms have been omitted for clarity with the exception of those on N4. Selected bond lengths (Å) and angles (deg): P1−O1 = 1.4793(10), P1−C1 = 1.7770(12). P1−C2 = 1.8287(13), P1−C3 = 1.8267(13), C1−C7 = 1.3707(16), C7−N4 = 1.3591(15), N1−C4 = 1.4722(15), N2−C4 = 1.4728(16), P1−C1− C7 = 135.33(9), P1−C1−N1 = 109.18(8), C7−C1−N1 = 115.47(10), C1−C7−N4 = 119.37(11), C8−C7−C1 = 125.37(11), C8−C7−N4 = 115.21(10), ∑∠C1 = 359.98, ∑∠C7 = 359.95.
Figure 1. Thermal ellipsoid representation (50% probability), of one of the two molecules in the asymmetric unit, for PTA CNH2(C6H5), 1, with the atomic numbering scheme. Hydrogen atoms have been omitted for clarity with the exception of those on N4. Selected bond lengths (Å) and angles (deg): P1−C1 = 1.8116(13), P1−C2 = 1.8713(13), P1−C3 = 1.8684(13), C1−C7 = 1.3597(17), C7−N4 = 1.3851(17), N1−C4 = 1.4750(16), N2−C4 = 1.4704(16), P1−C1−C7 = 126.23(10), P1−C1−N1 = 116.53(8), N1−C1−C7= 116.89(11), C1−C7−N4 = 121.76(12), C8−C7−C1 = 123.57(12), C8−C7−N4 = 114.65(11), ∑∠C1 = 359.65, ∑∠C7 = 359.98.
E-enamine isomer and crystallized in the monoclinic space group P21/c. The P1C1 bond lengths, 1.8116(13), 1.8152(11) and 1.7770(12) Å for 1, 3, and 8a, respectively, are shorter than for PTA (1.866 Å)40 and slightly shorter than for OPTA (1.817 Å).41,42 The P1C2 and P1C3 bonds are slightly elongated relative to those in PTA. These perturbations are caused by the presence of CC on the PTA cage. The C1C7 bond lengths for 1, 3, and 8a, 1.3597(17), 1.3540(14), and 1.3707(16) Å, respectively, are typical of CC double bonds. The ∑∠C1 and ∑∠C7 for all three complexes total ∼360° indicating sp2 hybridization and together with the bond length data confirm the enamine tautomer. Selected bond lengths and angles are listed in Figures 1−3. Additional structural data along with calculated structures are described in the Supporting Information. The stability of enamines 1−4 toward oxidation varies slightly with changes in R group and is similar to other PTA derivatives. In the solid state, 1−4 oxidize slowly with ∼15% oxidation upon exposure to air for one month. Oxidation in solution is more rapid; in chlorinated solvents 3 is completely oxidized at room temperature over the course of a month. Compounds 1, 2, and 4 are more stable than 3 with ∼25%, 40%, and 60% oxidation, respectively, observed after one month in chlorinated solvent. Chemical oxidation of 1−4 was accomplished by reaction of the phosphine with 30% H2O2 yielding a 55/45 mixture of E and Z isomers of the corresponding oxides 5−8 (Scheme 3). The oxides were characterized by multinuclear NMR spectroscopy (1H, 13C{1H}, and 31P{1H}) as well as IR spectroscopy. The 31P{1H} spectra of 5−8 contain two singlets between 0.5 and −5.5 ppm assigned to the E (5a−8a) and Z (5b−8b) isomers of the oxidized enamines. The NH2 protons are observed via 1H NMR spectroscopy as two singlets at ∼4.8 and 4.7 ppm
Figure 2. Thermal ellipsoid representation (50% probability), of one of the two molecules in the asymmetric unit, for PTA CNH2(C6H4OMe), 3, with the atomic numbering scheme. Hydrogen atoms have been omitted for clarity with the exception of those on N4. Selected bond lengths (Å) and angles (deg): P1−C1 = 1.8152(11), P1−C2 = 1.8635(11), P1−C3 = 1.8722(11), C1−C7 = 1.3540(14), C7−N4 = 1.3881(14), N1−C4 = 1.4792(15), N2−C4 = 1.4608(14), P1−C1−C7 = 124.12(8), P1−C1−N1 = 116.69(7), C7−C1−N1 = 117.90(10), C1−C7−N4 = 121.69(10), C8−C7−C1 = 122.13(10), C8−C7−N4 = 116.01(9), ∑∠C1 = 358.71, ∑∠C7 = 359.83.
C
DOI: 10.1021/acs.inorgchem.8b01167 Inorg. Chem. XXXX, XXX, XXX−XXX
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Inorganic Chemistry Scheme 3
Scheme 4
resulting from the E and Z isomers. The IR spectra of the oxides contain two sets of NH2 stretches; the IR spectrum of 6, for example, contains absorbances assigned to the NH2 group at 3419, 3367, 3291, and 3143 cm−1. A strong peak assigned to υ(PO) was observed via IR spectroscopy at 1149, 1167, 1174, and 1165 cm−1 for 5−8, respectively. The υ(PO) can be compared to the parent OPTA which exhibits an IR absorption at 1167 cm−1 in the solid state (KBr).10,43 Recrystallization of the mixture of E and Z isomers from chloroform/hexane resulted in ∼90% yield of the E isomer indicating E−Z isomerization is facile (i.e., the E isomer is not obtained due to selective crystallization). Using 31P{1H} NMR spectroscopy to monitor the conversion of 5a to 5b in CDCl3, equilibrium was obtained in ∼2.5 h at room temperature (Figure 4). No evidence of E−Z isomerization of phosphines
Table 2. DFT Calculations (B3LYP/LANL2DZ) of the Isomers/Tautomers of Phosphines (1−4) and Oxidesa (5− 8)
a
Values in parentheses are for the corresponding oxides.
to be ca. 2.2−2.6 kcal/mol lower in energy relative to the Zenamines and 7.9−9.7 kcal/mol lower in energy relative to the imine tautomers. DFT calculations performed for the various isomers of the oxides (5−8) revealed the Z-enamines, 5b−8b, to be favored by ∼3.0−3.2 kcal/mol relative to E-enamines 5a−8a and 12.1−12.5 kcal/mol relative to the respective imine tautomers. From a mechanistic point of view, nucleophilic attack by PTA-Li on the nitrile carbon (followed by aqueous workup) likely results in formation of the imine which tautomerizes to the more stable E-enamine form. The relative stability of the imine and enamine tautomers varies with substituent and solvent with the imine tautomer generally favored in unsubstituted systems.44−48 Conjugative stabilization of the olefin favors the enamine tautomer.44 The enamine tautomer also appears to be favored when the substituents on the olefin are more electron-withdrawing than those on nitrogen.46 The coordination chemistry of ligands 1−4 was explored via reaction with W(CO)4(pip)2. Upon coordination to the tungsten center the ligand tautomerizes to the imine form providing a strong chelating ligand. The κ2-P,N complexes 9− 12 were synthesized in moderate to good yield (58−87%) by the reaction of 1−4 with W(CO)4pip2 at 65 °C in toluene or 55 °C in CHCl3 over 12−72 h (Scheme 5). Complexes 9 and 11 were soluble in toluene and isolated as bright yellow powders by evaporation of solvent followed by recrystallization from CH2Cl2 and hexane. Complex 12 was insoluble in toluene and was obtained as a bright yellow powder by filtration of the reaction mixture. Complex 10 was isolated as a dark yellow powder by reaction of 2 with W(CO)4pip2 in CHCl3 followed
Figure 4. Isomerization of 5a to 5b in CDCl3 at room temperature.
1−4 was observed. We attribute the facile isomerization of the oxides versus the phosphines to resonance (Scheme 4). Evidence for the resonance argument can be obtained from the crystal structures discussed previously. The P1−C1 distance in the phosphine oxide 8a (Figure 4) is significantly shorter (1.7770 Å) than the P1−C2 and P1−C3 distances (1.8287 and 1.8267 Å, respectively). In addition the C7−N4 distance in 8a (1.359 Å) is shorter than the C7−N4 distance in 1 (1.385 Å) or 3 (1.388 Å). To gain further insight into the stability of various potential products of the reaction of PTA-Li with nitriles (imine, Eenamine, or Z-enamine), DFT calculations were performed at the B3LYP level of theory utilizing the LANL2DZ/6-31G* basis set. The relative energies of the E- and Z-enamines and the imine tautomers of 1−4 are depicted in Table 2. Consistent with our experiments, the E-enamines were found D
DOI: 10.1021/acs.inorgchem.8b01167 Inorg. Chem. XXXX, XXX, XXX−XXX
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Inorganic Chemistry 3
JPC = 6.7 Hz), and 69.1 (d, 3JPC = 6.7 Hz) for the PTA carbons. The chemical shifts and coupling constants of the carbonyl carbons correlate well with known values. The 2JPC for the carbonyl trans to phosphorus (2JPC ∼ 34 Hz) is significantly larger than for the carbonyl trans to nitrogen (2JPC ∼ 4 Hz). The resonance of the α-substituted carbon atom is shifted from 149.6 (sp2 C, d 1JPC = 33.6 Hz) in 1 to 70.9 (d, 1 JPC = 15.8 Hz, sp3 C) in 9 while that of the β-carbon atom is shifted from 115.7 (CCN) in 1 to 184.8 (CCN) in 9. These shifts are indicative of a change in ligand structure from enamine to imine. The 1H and 13C{1H} NMR spectra of 10−12 are similar to 9 (see Supporting Information and Experimental Section for more details). In order to examine the tautomerization of the ligands upon coordination to the tungsten center, the synthesis of complexes 9−12 was performed at lower temperature. The reactions of 1−4 with W(CO)4pip2 in CH2Cl2 or toluene at 35 °C resulted in a mixture of 3 products (Scheme 5). For example, in the reaction of 3 with W(CO)4pip2 in toluene at 35 °C the 31 1 P{ H} NMR spectrum contained resonances at −38 (1JPW = 217 Hz), −68 (1JPW = 212 Hz), and −70 (1JPW = 214 Hz) ppm. The ratio of the products depends on the ligand, temperature, reaction time, and solvent. The reaction of 1 with W(CO)4pip2 in CD2Cl2 was monitored by 31P{1H} NMR spectroscopy at room temperature for 1 h. A peak at −68 ppm appeared almost immediately followed by a resonance at −70 ppm after approximately 20 min. Finally, a peak at −38 ppm was observed corresponding to the κ2-P,N imine complex described above. On the basis of various spectroscopic data and a fortuitous crystal structure we speculate the three compounds are the κ2-P,N imine, κ1-P imine, and κ1-P enamine. A crystal structure of 11a revealed that the peak at −67.8 ppm (1JPW = 218 Hz) is the κ1-P enamine complex (vide infra). Isolated samples of 9a or 9b convert to 9 upon heating in dichloromethane over a couple hours. On the basis of a sharp IR stretch in the imine region (υ(NH) = 3216 cm−1), the peak at −70 ppm appears for the κ1-P imine complex prior to displacement of piperidine and chelation (9b). On the basis of the data above we speculate that the change in coordination mode from κ1-P to κ2-P,N appears to be preceded by tautomerization of the enamine to the imine. Yellow crystals of 9 were obtained by the slow evaporation of a methanol solution of 9 at room temperature. X-ray quality crystals of 12 were grown by slow evaporation of 1:1 hexane/ dichloromethane solution of 12 at −10 °C. Compounds 9 and 12 (Figures 5 and 6) each have a distorted octahedral geometry with pseudo-C2v symmetry (further confirmed by IR spectroscopy). The C11−C5 bond lengths of 1.513(6) and 1.502(12) Å for 9 and 12, respectively, are typical of CC single bonds while the C11N4 bond lengths of 1.274(6) and 1.278(11) Å for 9 and 12 are typical of CN double bonds. The W1P1 distances of 2.4681(11) Å (9) and 2.451(7) Å (12), and the W1N4 bond lengths of 2.223(4) Å for 9 and 2.239(7) for 12, are slightly shorter than those reported for similar κ2-P,N tungsten tetracarbonyl compounds such as [W(CO)4(PPh2py)], WP = 2.543 Å and WN = 2.256 Å, or [W(CO)4(P(NMe2)2py)], WP = 2.507 Å and WN = 2.273 Å.49,51 The W1C1 bond trans to phosphorus is slightly shorter (1.948 Å) than the W1C2 bond trans to the imine nitrogen (1.973 Å) in 9. In 12 the methoxy substituents alter the electronics such that the W1C1 distance is elongated, relative to 9, to 1.974 Å, and the W1C2 distance
Scheme 5
by recrystallization from CH2Cl2 and hexanes. The synthesis of complex 10 in toluene resulted in a mixture of the κ1-P and κ2P,N complexes. All four tungsten complexes (9−12) are soluble in chloroform, dichloromethane, methanol, ethanol, and acetone and insoluble in hexane and water. Complexes 9−12 were characterized by 31P{1H}, 1H, 13C1 { H}, and HMQC NMR spectroscopy, IR spectroscopy, HRMS, and X-ray crystallography (9 and 12). The 31P{1H} NMR spectra for each compound contain a single resonance with tungsten satellites: −38.9 ppm (1JPW = 217.4 Hz) for 9, −37.4 ppm (1JPW = 210.6 Hz) for 10, −38.7 ppm (1JPW = 217.4 Hz) for 11, and −38.1 ppm (1JPW = 217.5 Hz) for 12. The coupling constants (1JPW) are consistent with those reported for W(CO)4(PTA)2 (1JPW = 216 Hz)17 and slightly larger than the previously reported W(CO)4PTA-PPh2 (1JPW = 201)17 and W(CO)5(PPh2py) (1JPW = 196 Hz).49 The carbonyl stretching frequencies of 9−12, obtained by IR spectroscopy, are observed at lower wavenumbers than tungsten complexes of PTA, PTA-PPh2, PPh3, DPPM, or PPh2Py indicating that 1−4 are more electron-donating than those ligands, Table 3. Table 3. Solid State IR Data of W(CO)4L2 Complexes, υ(CO), cm−1 [W(CO)4(PTA-PPh2)]17 [W(CO)4(PPh3)(PTA)]17 [W(CO)4(PTA)2]17 [W(CO)4(PPh3)2]17 [W(CO)4(DPPM)]17 [W(CO)5(PPh2py)]49 [W(CO)5(P(NMe2)2py)]49 9 10 11 12
2018 2017 2018 2018 2018 2017 2002 2005 2013 2005 2008
1916 1913 1917 1939 1916 1890 1890 1887 1908 1863 1878
1899 1898 1900 1907 1904 1870 1871 1863 1869 1849 1856
1881 1879 1883 1889 1974 1826 1840 1829 1814 1820 1828
Formation of the tungsten complexes and tautomerization of the ligand to the imine form leads to formation of a chiral center further reducing the symmetry of the PTA cage. The 1H NMR spectra of complexes 9−12 are non-first-order. Worth noting is the methine proton (PCHN) of the PTA cage at 4.78−4.94 ppm, and the NH proton at 9.79−10.08 ppm (3JPH = 7.3−7.9 Hz). There is no 4JPH coupling observed between phosphorus and the amine protons (NH2) in 1−4. Unlike the NH2 protons in the free ligands, which are exchangeable with D2O, the NH protons of the κ2-complexes do not readily exchange with D2O, presumably due to the lack of an available lone pair on nitrogen indicative of strong coordination of the imine to the metal center.50 The 13C{1H} NMR spectrum of 9 contains the following: two PCH2N resonances, 54.1 ppm (d, 1 JPC = 1.5 Hz) and 54.0 ppm (d, 1JPC = 2.2 Hz); a PCHN resonance at 70.9 ppm, α-carbon (d, 1JPC = 15.8 Hz); and three NCH2N resonances at 75.3 (d, 3JPC = 3.1 Hz), 72.6 (d, E
DOI: 10.1021/acs.inorgchem.8b01167 Inorg. Chem. XXXX, XXX, XXX−XXX
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Inorganic Chemistry
(1.844 and 1.846 Å in 9 and 1.844 and 1.850 Å in 12) similar to other α-substituted PTA derivatives.17,19−21 This elongation of the P1C5 bond relative to the other PC bonds is in contrast with the observation in the free ligands, which exist in the enamine form, and 11a (vide infra) where the PC bond of the substituted carbon is shorter than the other PC bonds. The solid state structure of the κ1-P 11a (Figure 7) reveals that the ligand maintains its E-enamine configuration upon
Figure 5. Thermal ellipsoid representation (50% probability) of 9 with the atomic numbering scheme. Hydrogen atoms have been omitted for clarity. Selected bond lengths (Å) and angles (deg): W1− P1 = 2.4681(14), W1−N4 = 2.223(5), W1−C1 = 1.948(6), W1−C2 = 1.973(6), W1−C3 = 2.034(6), W1−C4 = 2.022(6), P1−C5 = 1.870(6), P1−C6 = 1.844(6), P1−C7 = 1.846(6), C5−C11 = 1.513(8), N4−C11 = 1.274(7), N1−C9 = 1.466(8), N2−C10 = 1.459(8), P1−W1−N4 = 71.59(13), N4−W1−C2 = 178.5(2), C1− W1−C2 = 90.8(3), C3−W1−C4 = 173.4(2), C2−W1−C3 = 86.6(2), C2−W1−C4 = 86.8(2), P1−C5−C11 = 106.2(4), P1−C5−N1 = 113.2(4), C11−C5−N1 = 116.2(5), C5−C11−C12 = 122.1(6), C5− C11−N4 = 115.7(6), N4−C11−C12 = 122.0(6), ∑∠C5 = 335.6, ∑∠C11 = 359.8.
Figure 7. Thermal ellipsoid representation (50% probability) of 11a with the atomic numbering scheme. Hydrogen atoms, with the exception of those on heteroatoms, have been omitted for clarity. Selected bond lengths (Å) and angles (deg): W1−P1 = 2.5480(7), W1−N5 = 2.320(2), W1−C1 = 1.973(2), W1−C2 = 1.954(3), W1− C3 = 2.043(6), W1−C4 = 2.027(6), P1−C5 = 1.821(3), P1−C6 = 1.864(3), P1−C7 = 1.863(3), C5−C11 = 1.352(4), N4−C11 = 1.376(4), N1−C10 = 1.479(4), N2−C9 = 1.476(4), P1−W1−N5 = 94.78, N5−W1−C2 = 179.01(11), C1−W1−C2 = 85.51(11), C3− W1−C4 = 172.70(14), C2−W1−C3 = 88.91(17), C2−W1−C4 = 85.95(15), P1−C5−C11 = 130.8(2), P1−C5−N1 = 113.19(19), C11−C5−N1 = 115.6(3), C5−C11−C12 = 126.7(3), C5−C11−N4 = 119.9(3), N4−C11−C12 = 113.4(3), ∑∠C5 = 359.59, ∑∠C11 = 360.0.
coordination to a metal center. The C5C11 distance of 1.363(12) Å is typical of a CC bond and slightly longer than the same bond in the free ligand (3), 1.3540 Å. The C11N4 distance of 1.374(12) Å is typical of a CN single bond and slightly shorter than the 1.3881 Å distance observed in 3. This change in CC and CN distances is similar that that observed in the oxide where tautomerization was more facile than in the free phosphine ligands. The W1P1 and WN distances in the κ2-P,N complexes 9 (2.4681 and 2.223 Å, respectively) and 12 (2.451 and 2.239 Å, respectively) are much shorter than that of the κ1-P complex 11a (2.5480 and 2.3197 Å, respectively).
Figure 6. Thermal ellipsoid representation (50% probability) of 12 with the atomic numbering scheme. Hydrogen atoms, with the exception of those on N4 and C5, have been omitted for clarity. Selected bond lengths (Å) and angles (deg): W1−P1 = 2.451(2), W1−N4 = 2.239(7), W1−C1 = 1.974(11), W1−C2 = 1.960(11), W1−C3 = 2.041(11), W1−C4 = 2.051(10), P1−C5 = 1.857(8), P1− C6 = 1.844(9), P1−C7 = 1.850(10), C5−C11 = 1.501(12), N4−C11 = 1.277(11), N1−C9 = 1.476(12), N2−C10 = 1.469(12), P1−W1− N4 = 73.1(2), N4−W1−C2 = 173.6(3), C1−W1−C2 = 88.1(4), C3−W1−C4 = 174.1(4), C2−W1−C3 = 88.5(4), C2−W1−C4 = 90.9(4), P1−C5−C11 = 108.1(6), P1−C5−N1 = 112.5(6), C11− C5−N1 = 117.3(7), C5−C11−C12 = 122.2(8), C5−C11−N4 = 114.5(8), N4−C11−C12 = 123.2(8), ∑∠C5 = 337.9, ∑∠C11 = 359.9.
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CONCLUSIONS New PTA derivatives have been successfully synthesized by insertion of nitriles into the C−Li bond of LiPTA to afford an enamine with an sp2-carbon on the PTA cage. The free ligand is stable in water and does not appear to undergo either E−Z isomerization or tautomerization. The oxides of ligands readily undergo E−Z isomerization, presumably through an imine intermediate resulting from tautomerization. Tungsten tetracarbonyl complexes of the enamine ligands reveal various
is reduced to 1.960 Å. This appears to indicate increased electron donation from the imine relative to 9. A PTA cage distortion is observed with P1C5 (1.870 Å in 9 and 1.857 Å in 12) slightly longer than the P1C6 and P1C7 distances F
DOI: 10.1021/acs.inorgchem.8b01167 Inorg. Chem. XXXX, XXX, XXX−XXX
Article
Inorganic Chemistry coordination modes: κ1-P (enamine), κ1-P (imine), and κ2-P,N (imine). Tautomerization of the enamine to a chiral imine appears to occur after coordination to the metal center. We have started to explore the ability of the κ2-P,N (imine) complexes to ring open as well as stability toward deprotonation.
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crystals were grown by slow evaporation of a 1:1 dichloromethane/ hexane solution of PTAC(NH2)(C6H5) at −10 °C over 4 days. Synthesis of PTAC(C6H4Me)NH2, 2. 4-Methylbenzonitrile (0.23 mL, 1.92 mmol) was added dropwise via syringe to a suspension of PTA-Li (0.31 g, 1.92 mmol) in 30 mL of distilled THF in a dry ice/ acetone bath (−78 °C). After stirring at room temperature for approximately 4 h, a thick yellow suspension formed. Upon addition of cold water (0.03 mL, 1.90 mmol), a clear solution was obtained. The solvent was removed under vacuum resulting in a white solid. The solid was washed with cold water, to remove PTA and LiOH, and diethyl ether to remove excess nitrile. The solid was then dissolved in 1 mL of dichloromethane and precipitated by addition of 10 mL of hexane providing 0.53 g of 2 as white solid (91% yield). 1H NMR (400 MHz, CDCl3) δ 7.25−7.19 (m, 3H, ArH), 7.14 (d, 1H, ArH), 4.78, 4.46 (AB spin system, 2JHAHB = 13.0 Hz, 4H NCH2N), 4.68, 4.54 (AB spin system, 2JHAHB = 13.2 Hz 2H, NCH2N), 4.36 (br, s, 2H, NH2), 3.86−3.72 (m, 4H, PCH2N). 13C{1H} NMR (100 MHz, CDCl3) δ 149.6 (d, 1JPC = 33.7 Hz, C1), 137.6 (s, C11), 136.2 (d, 3 JPC = 4.3 Hz, C8), 129.5 (d, 4JPC = 4.4 Hz, C9), 129.4 (s, C12), 127.8.0 (s, C10), 115.2 (d, 2JPC = 12.6 Hz, C7), 74.6 (d, 3JPC ∼ 0 Hz, C4,6), 73.7 (d, 3JPC ∼ 0 Hz, C5), 52.8 (d, 1JPC = 17.7 Hz, C2,3), 21.4 (s, C14). 31P{1H} NMR (162 MHz, CDCl3) −87.3 (s). 31P{1H} NMR (162 MHz, D2O) −87.83 (s). Solid state IR (cm−1): υ(NH2) 3372 (asymmetric), 3277 (symmetric); υ(CC) 1621. HRMS (ESI, CH3OH) m/z for C14H20N4P [M + H+]: calcd 275.1426; found 275.1435. Synthesis of PTAC(C6H4OMe)NH2, 3. A suspension of PTA-Li (1.20 g, 7.36 mmol) in 30 mL of distilled THF was cooled in a dry ice/acetone bath at −78 °C. A solution of 4-methoxylbenzonitrile (0.98 g, 7.36 mmol) in 30 mL of THF was added slowly via cannula. After stirring at room temperature for approximately 4 h, a thick yellow suspension formed. Upon addition of cold water (0.13 mL, 7.36 mmol), a clear solution was obtained. The solvent was removed under vacuum resulting in a white solid. The solid was washed with cold water, to remove PTA and LiOH, and diethyl ether to remove excess nitrile. The residual solid was dissolved in 1 mL of dichloromethane and was precipitated by addition of 10 mL of hexane resulting in 1.05 g of 3 as a white solid (49% yield). 1H NMR (400 MHz, CDCl3) 7.38 (d, J = 7.8 Hz, 2H, ArH), 6.89 (d, J = 8.7 Hz, 2H, ArH), 4.81, 4.46 (AB spin system, 2J(HAHB)= 12.7 Hz, 4H, NCH2N), 4.72, 4.58 (AB spin system, 2J(HAHB) = 13.1 Hz, 2H, NCH2N), 4.33 (br, s, 2H, NH2), 3.92−3.72 (m, 4H PCH2N), 3.80 (s, 3H, OCH3). 13C{1H} NMR (100 MHz, CDCl3) δ 159.9 (s, C11), 149.2 (d, 1JPC = 33.4 Hz, C1), 130.3 (d, 4JPC = 5.5 Hz, C9,13), 128.6 (d, 3JPC = 4.4 Hz, C8), 114.9 (d, 2JPC = 11.8 Hz, C7), 113.4 (s, C10,12), 74.7 (d, 3JPC = 1.6 Hz, C4,5), 73.9 (d, 3JPC = 2.8 Hz, C6), 55.2 (s, C15), 52.7 (d, 1JPC = 17.6 Hz, C2,3). 31P{1H} NMR (162 MHz, CDCl3) δ −86.8 (s). 31P{1H} NMR (162 MHz, D2O) −87.52 (s). Solid state IR (cm−1): υ(NH2) 3324 (asymmetric), 3309 (symmetric); υ(CC) 1617. HRMS (ESI, CH3OH) m/z for C14H20N4OP [M + H+]: calcd 291.1374; found 291.1450. X-ray quality crystals were grown by slow evaporation of a 1:1 dichloromethane/hexane solution of PTAC(NH2)(C6H4OMe) in a freezer for 2 weeks. Synthesis of PTAC(C6H2(OMe)3NH2), 4. A solution of 3,4,5trimethoxylbenzonitrile (0.50 g, 2.58 mmol) in 30 mL of THF was added slowly via cannula to a suspension of PTA-Li (0.42 g, 2.58 mmol) in 30 mL of distilled THF in a dry ice/acetone bath. Upon addition, the reaction mixture immediately turned light yellow. The resulting yellow suspension was stirred at −78 °C for 30 min and warmed to room temperature after which stirring was continued until a thick yellow suspension was formed (approximately 4 h). Upon addition of cold water (0.05 mL, 2.58 mmol), a clear solution was obtained. The solvent was removed under vacuum resulting in a white solid. The solid was washed with cold water, to remove PTA and LiOH, followed by diethyl ether to remove excess nitrile. The resulting solid was recrystallized by dissolving in 1 mL of dichloromethane followed by precipitation by addition of 10 mL of hexanes resulting in 0.52 g of 4 as a white solid (57% yield). 1H NMR (400 MHz, CDCl3) δ 6.69 (s, 2H, ArH), 4.82, 4.49 (AB aspin system,
EXPERIMENTAL SECTION
Materials and Methods. Unless otherwise noted, all manipulations were performed on a double-manifold Schlenk vacuum line under nitrogen or in a nitrogen-filled glovebox. Tetrahydrofuran (THF) was freshly distilled under nitrogen from sodium/ benzophenone. Dichloromethane and chloroform were degassed and dried with activated molecular sieves. Water was distilled and deoxygenated before use. NMR solvents were purchased from Cambridge Isotopes and used as received. Tetrakis(hydroxymethyl)phosphonium chloride was obtained from Cytec or Rhodia and used without further purification. 1,3,5-Triaza-7-phosphaadamantane (PTA),39 PTA-Li,17 and cis-[W(CO)4(pip)2]52 were synthesized as reported in the literature. NMR spectra were recorded with Varian Unity Plus 500 FT-NMR or Varian NMR System 400 spectrometer. 1 H and 13C{1H} NMR spectra were referenced to residual solvent relative to tetramethylsilane (TMS). Phosphorus chemical shifts are relative to an external reference of 85% H3PO4 in D2O with positive values downfield of the reference. Solid state IR spectra were recorded on a Nicolet 6700 FT-IR spectrometer. X-ray crystallographic data were collected at 100(±1) K on a Bruker APEX CCD diffractometer with Mo Kα radiation (λ = 0.71073 Å) and a detector-to-crystal distance of 4.94 cm. Data collection was optimized utilizing the APEX 2 software with 0.5° rotation between frames. Data integration, correction for Lorentz and polarization effects, and final cell refinement were performed using SAINTPLUS and corrected for absorption using SADABS. The structures were solved by direct methods and refined using SHELXTL, version 6.10.53 Crystallographic data, data collection parameters, and a complete list of bond lengths and angles may be found in the Supporting Information. Theoretical calculations using Gaussian were carried out at the B3LYP level of density function theory (DFT) adopting the LANL2DZ/631G* basis set.54 Caution! PTA-Li is a highly pyrophoric solid, igniting violently upon exposure to air. Synthesis of PTAC(C6H5)NH2, 1. Benzonitrile (0.16 mL, 1.90 mmol) was added dropwise via syringe to a −78 °C suspension of PTA-Li (0.31 g, 1.90 mmol) in 30 mL of distilled THF. The resulting yellow suspension was stirred for 30 min at −78 °C and allowed to warm to room temperature. After stirring at room temperature for approximately 4 h, a thick yellow suspension formed. Upon addition of cold water (0.03 mL, 1.90 mmol), a clear solution was obtained. The solvent was removed under vacuum resulting in a white solid. The solid was washed with cold water, to remove PTA and LiOH, and diethyl ether to remove excess nitrile. The residual solid was dissolved in 1 mL of dichloromethane and crashed out with 10 mL of hexane resulting in 0.20 g of 1 as a white solid (60% yield) after filtration. 1H NMR (400 MHz, CDCl3) δ 7.44 (dd, J = 6.4, 1.6 Hz, 2H, ArH), 7.40−7.32 (m, 3H, ArH), 4.82, 4.50 (AB spin system, 2J(HAHB) = 12.6 Hz, 4H, NCH2N), 4.73, 4.59 (AB spin system, 2J(HAHB) = 13.1 Hz, 2H, NCH2N), 4.35 (br, s, 2H, NH2), 3.92−3.73 (m, 4H, PCH2N). 13 C{1H} NMR (100 MHz, CDCl3) δ 149.6 (d, 1JPC = 33.6 Hz, C1), 136.3 (d, 3JPC = 4.3 Hz, C8), 129.1 (d, 4JPC = 5.2 Hz, C9,13), 128.7 (s, C11), 128.0 (s, C10,12), 115.7 (d, 2JPC = 12.9 Hz, C7), 74.8 (d, 3 JPC = 1.7 Hz, C4,5), 73.9 (d, 3JPC = 2.8 Hz, C6), 52.8 (d, 1JPC = 17.7 Hz, C2,3). 13C{31P} NMR (126 MHz, CDCl3) δ 149.6 (s, C1), 136.3 (s, C8), 129.1(s, C9,13), 128.7 (s, C11), 128.0 (s, C10,12), 115.4 (s, C7), 74.7 (s, C4,5), 73.8 5(s, C6), 52.7 (s, C2,3). 31P{1H} NMR (162 MHz, CDCl3) δ −87.1 (s). 31P{1H} NMR (162 MHz, D2O) −88.04 (s). Solid state IR (cm−1): υ(NH2) 3369 (asymmetric), 3280 (symmetric); υ(CC) 1625. HRMS (ESI, CH3OH) m/z for C13H18N4P [M + H+]: calcd 261.1269; found 261.1261. X-ray quality G
DOI: 10.1021/acs.inorgchem.8b01167 Inorg. Chem. XXXX, XXX, XXX−XXX
Article
Inorganic Chemistry
Hz, C4,5, Z), 73.3 (d, 3JPC = 7.5 Hz, C4,5, E), 72.7 (d, 3JPC = 9.3 Hz, C6, Z), 72.5 (d, 3JPC = 9.4 Hz, C6, E), 57.8 (d, 1JPC = 57.7 Hz, C2,3, E), 57.4 (d, 1JPC = 54.2 Hz, C2,3, Z), 55.2 (s, C14, Z), 55.2 (s, C14, E). 31P{1H} NMR (162 MHz, CDCl3) δ 0.7 (s, Z), −5.2 (s, E). Solid state IR (cm−1): υ(NH) 3423, 3310, 3181; υ(CC) 1606; υ(PO) 1174. HRMS (ESI, CH3OH) m/z for C14H20N4O2P [M + H+]: calcd 307.1324; found 307.1318. OPTAC(Ph(OMe)3)NH2, 8. 1H NMR (400 MHz, CDCl3) δ 6.81 (s, 1H, Ar, E), 6.66 (s, 1H, Ar, Z), 4.86−4.76 (2H NH2), 4.53−4.35 (m, 5H, NCH2N), 4.18−4.06 (m, 5H, NCH2N), 3.89−3.81 (m, 11H, 2NCH2N, 9 CH3), 3.73−3.63 (m, 4H, PCH2N). 13C{1H} NMR (100 MHz, CDCl3) δ 154.8 (d, 1JPC = 11.8 Hz, C1, Z), 153.7 (d, 1JPC = 18.7 Hz, C1, E), 152.8 (s, C11, Z), 152.3 (s, C11, E), 139.3 (s, C10,12, E), 138.7 (s, C10,12, Z), 131.2 (d, 3JPC = 11.3 Hz, C8, Z), 129.0 (d, 3JPC = 2.6 Hz, C8, E), 111.7 (d, 2JPC = 103.1 Hz, C7, E), 109.3 (d, 2JPC = 90.7 Hz, C7, Z), 106.7 (s, C9,13 Z), 105.5 (s, C9,13, E), 74.6 (d, 3JPC = 8.1 Hz, C4,5, Z), 73.3 (d, 3JPC = 7.5 Hz, C4,5, E), 72.8 (d, 3JPC = 9.3 Hz, C6, Z), 72.5 (d, 3JPC = 9.4 Hz, C6, E), 60.8 (s, C15, Z), 60.8 (s, C15, E), 57.9 (d, 1JPC = 57.7 Hz, C2,3, E), 57.5 (d, 1 JPC = 54.1 Hz, C2,3, Z), 56.2 (s, C14,16, Z), 56.2 (s, C14, 16, Z). 31 1 P{ H} NMR (162 MHz, CDCl3) δ 0.2 (s, Z), −5.4 (s, E). Solid state IR (cm−1): υ(NH) 3418, 3259, 3141; υ(CC) 1609; υ(PO) 1165. Synthesis of W(CO)4PTA-C(C6H5)NH, 9. To a 50 mL Schlenk flask containing 0.32 g (0.69 mmol) of W(CO)4(pip)2 and 0.18 g (0.69 mmol) of 1 was added 30 mL of degassed toluene via cannula resulting in a yellow suspension. The suspension was heated under nitrogen at 65 °C for 72 h. The resulting reddish brown solution was filtered through Celite and the solvent removed under vacuum. The resulting reddish brown solid was dissolved in 2 mL of dichloromethane and precipitated with hexane (∼20 mL) resulting in 0.26 g of 9 as a bright yellow powder (68% yield). 1H NMR (400 MHz, CDCl3) δ 10.08 (d, 3JPH = 7.3 Hz, 1H, NH), 7.66−7.59 (m, 2H, ArH), 7.58−7.53 (m, 1H, ArH), 7.49 (t, J = 7.5 Hz, 2H ArH), 4.87 (s, 1H, PCHN), 4.78 (dd, J = 58.6, 13.9 Hz, 2H, NCH2N), 4.57 (m, 1H, NCH2N), 4.54−4.46 (m, 2H, NCH2N), 4.27−4.16 (m, 1H NCH2N; 2H PCH2N), 3.78−3.64 (m, 2H, PCH2N). 13C{1H} NMR (100 MHz, CDCl3) 212.0 (d, 2JPC = 4.0 Hz, C2), 209.2 (d, 2JPC = 34.7 Hz, C1), 201.9 (d, 2JPC = 8.6 Hz, C3), 201.9 (d, 2JPC = 5.2 Hz, C4), 184.8 (d, 2JPC = 7.4 Hz, C11), 134.2 (d, 3JPC = 3.3 Hz C12), 132.3 (s, C15), 129.0 (s C13,17), 127.0 (s, C14,16), 75.3 (d, 3JPC = 3.1 Hz, C9), 72.6 (d, 3JPC = 6.7 Hz, C8), 70.9 (d, 2JPC = 15.8 Hz, C5), 69.1 (d, 3JPC = 6.7 Hz, C10), 54.1 (d, 1JPC = 1.6 Hz, C6), 54.0 (d, 1JPC = 2.2 Hz, C7). 31 1 P{ H} NMR (162 MHz, CD2Cl2) −38.9 (1JPW = 217.4 Hz). Solid state IR (cm−1): υ(NH) 3315; υ(CO) 2005, 1887, 1863, 1829. HRMS (ESI, CH3OH) m/z for C17H18N4O4PW [M + H+]: calcd 557.0575; found 557.0598. X-ray quality crystals were grown at room temperature by slow evaporation of a methanol solution of 9 over 7 days. Synthesis of W(CO)4PTA-C(C6H4Me)NH, 10. To a 50 mL Schlenk flask containing W(CO)4(pip)2 (0.39 g, 0.84 mmol) and 2 (0.23 g, 0.84 mmol) was added 30 mL of degassed chloroform via cannula providing a yellow suspension. The suspension was heated to 55 °C for 12 h under nitrogen resulting in a reddish brown solution. The solution was filtered through Celite and the solvent removed under vacuum. The resulting reddish brown solid was dissolved in 2 mL of dichloromethane and precipitated by addition of hexanes (∼20 mL) providing 0.42 g (0.74 mmol, 87% yield) of bright yellow 10 after filtration. 1H NMR (400 MHz, CD2Cl2) δ 9.99 (d, 3JPH = 7.8 Hz, 1H, NH), 7.48−7.46 (m, 2H, ArH), 7.21−7.19 (d, 3JPH = 7.6 Hz, 2H, ArH), 4.84 (s, 1H, PCHN), 4.78−4.61 (m 2H, NCH2N), 4.53−4.48 (dd, 3JPH = 5.0, 15.2 Hz, 2H, NCH2N), 4.21−4.01 (m, 1H (NCH2N); 2H PCH2N), 3.72−3.50 (m, 1H NCH2N; 2H, PCH2N). 13C{1H} NMR (100 MHz, CD2Cl2) 212.2 (d, 2JPC = 4.1 Hz, C2), 209.6 (d, 2 JPC = 34.2 Hz, C1), 202.1 (d, 2JPC = 8.5 Hz, C3), 202.0 (d, 2JPC = 5.3 Hz, C4), 184.7 (d, 2JPC = 7.2 Hz, C11), 143.1 (s, C15),131.3 (d, 3JPC = 3.2 Hz C12), 129.4 (s, C13,17), 127.1 (s, C14,16), 75.1 (d, 3JPC = 3.3 Hz, C9), 72.4 (d, 3JPC = 6.8 Hz, C8), 70.6 (d, 2JPC = 16.3 Hz, C5), 68.9 (d, 3JPC = 6.8 Hz, C10), 53.8 (s, C6), 53.8 (s, C7). 31P{1H}
2
J(HAHB) = 12.9 Hz, 4H, NCH2N), 4.73, 4.60 (AB spin system, J(HAHB) = 13.1 Hz, 2H, NCH2H), 4.37 (br, s, 2H, NH2), 3.86 (s, 6H, OCH3), 3.85 (s, 3H, OCH3), 3.95−3.76 (m, 4H, PCH2N). 13C{1H} NMR (100 MHz, CDCl3) δ 152.8 (s, C11), 149.6 (d, 1JPC = 32.9 Hz, C1), 138.2 (s, C10,12), 131.5 (d, 3JPC = 4.2 Hz, C8), 115.5 (d, 2JPC = 13.5 Hz, C7), 106.3 (d, 4JPC = 5.7 Hz, C9,13), 74.6 (d, 3JPC = 1.5 Hz, C4,5), 73.8 (d, 3JPC = 2.7 Hz, C6), 60.8 (s, C14,16), 56.1 (s, C15), 52.7 (d, 1JPC = 18.0 Hz, C2,3). 31P{1H} NMR (162 MHz, CDCl3) −87.9 (s). 31P{1H} NMR (162 MHz, D2O) −87.74 (s). Solid state IR (cm−1): υ(NH2) 3460 (asymmetric), 3340 (symmetric); υ(CC) 1603. HRMS (ESI, CH3OH) m/z for C16H24N4O3P [M+H+]: calcd 351.1586; found 351.1578. X-ray quality crystals of OPTA C(NH2)(C6H2(OMe)3) were grown by slow evaporation of a 1:1 dichloromethane/hexane solution of PTAC(NH2)(C6H2(OMe)3) in a freezer for 4 weeks. Synthesis of OPTAC(R)NH2, 5−8. Oxides of compounds 1−4 were synthesized by charging a Schlenk flask with the ligand in 20.0 mL of THF. To the solution was added 0.3 mL of 30% H2O2 solution. The resulting white suspension was stirred at room temperature for 15 min, providing a clear solution. The solvent was removed under vacuum, and the resulting white solid was dissolved in minimum amount of dichloromethane and precipitated using hexane. The resulting white solid was dried, and the oxides 5−8 were obtained in near quantitative yield. The oxides were isolated as a mixture of Z and E isomers. OPTAC(Ph)NH2, 5. 1H NMR (400 MHz, CDCl3) δ 7.54−7.51 (m, 2H, Ar), 7.41−7.35 (m, 3H, Ar), 4.86−4.75 (2H NH2), 4.51− 4.48 (m, 2H, NCH2N), 4.45−4.41 (m, 1H, NCH2N), 4.37−4.30 (m, 2H, NCH2N), 4.15−4.09 (m, 4H, NCH2N), 4.07−4.02 (m, 1H, NCH2N), 3.93−3.86 (m, 1H, NCH2N), 3.81−3.73 (m, 1H, NCH2N), 3.68−3.63 (m, 4H, PCH2N). 13C{1H} NMR (100 MHz, CDCl3) δ 155.0 (d, 1JPC = 11.7 Hz, C1, Z), 153.5 (d, 1JPC = 19.4 Hz, C1, E), 135.9 (d, 3JPC = 11.2 Hz, C8, Z), 134.1 (d, 3JPC = 2.6 Hz, C8, E), 129.7 (s, C10,12, E), 129.2 (s, C10,12, Z), 128.9 (d, 4JPC = 1.0 Hz, C9,13 Z), 128.1 (d, 4JPC = 2.6 Hz, C9,13, E), 127.7 (s, C11), 111.4 (d, 2 JPC =104.2 Hz, C7, Z), 108.9 (d, 2JPC =91.28 Hz, C7, E), 74.6 (d, 3JPC = 8.1 Hz, C4,5, Z), 74.6 (d, 3JPC = 7.5 Hz, C4,5, E), 72.7 (d, 3JPC = 9.3 Hz, C6, Z), 72.4 (d, 3JPC = 9.4 Hz, C6, E), 57.8 (d, 1JPC = 57.7 Hz, C2,3, E), 57.4 (d, 1JPC = 54.1 Hz, C2,3, Z). 31P{1H} NMR (162 MHz, CDCl3) δ 0.5 (s, Z), −5.2 (s, E). Solid state IR (cm−1): υ(NH) 3431.6, 3364, 3282, 3147; υ(CC) 1612; υ(PO) 1149. HRMS (ESI, CH3OH) m/z for C13H18N4OP [M + H+]: calcd 277.1218; found 277.1226. OPTAC(PhMe)NH2, 6. 1H NMR (400 MHz, CDCl3) δ 7.43− 7.72 (m, 2H, Ar), 7.19−7.16 (t, 2H, Ar), 4.83−4.70 (2H NH2), 4.51− 4.47 (m, 2H, NCH2N), 4.45−4.42 (m, 1H, NCH2N), 4.37−4.31 (m, 2H, NCH2N), 4.16−4.03 (m, 5H, NCH2N), 3.93−9.86 (m, 1H, NCH2N), 3.81−3.73 (m, 1H, NCH2N), 3.69−3.62 (m, 4H, PCH2N), 2.37−2.35 (two s, 3H, CH3). 13C{1H} NMR (100 MHz, CDCl3) δ 155.1 (d, 1JPC = 11.7 Hz, C1, Z), 153.6 (d, 1JPC = 19.4 Hz, C1, E) 127.7 (s, C11, E), 139.3 (s, C11, Z), 133.0 (d, 3JPC = 11.1 Hz, C8, Z), 131.1 (d, 3JPC = 2.6 Hz, C8, E), 128.8 (d, 4JPC = 0.9 Hz, C9,13 Z), 128.8 (s, C9,13, E), 128.4 (s, C10,12, E), 128.0 (s, C10,12, Z), 111.1 (d, 2JPC =104.7 Hz, C7, Z), 108.6 (d, 2JPC =91.7 Hz, C7, E), 74.6 (d, 3 JPC = 8.1 Hz, C4,5, Z), 73.2 (d, 3JPC = 7.5 Hz, C4,5, E), 72.7 (d, 3JPC = 9.3 Hz, C6, Z), 72.4 (d, 3JPC = 9.4 Hz, C6, E), 57.7 (d, 1JPC = 57.7 Hz, C2,3, E), 57.4 (d, 1JPC = 54.1 Hz, C2,3, Z), 21.4 (s, C14). 31 1 P{ H} NMR (162 MHz, CDCl3) δ 0.5 (s, Z), −5.2 (s, E). Solid state IR (cm−1): υ(NH) 3419, 3367, 3292; υ(CC) 1611; 3143.5; υ(PO) 1167. OPTAC(PhOMe)NH2, 7. 1H NMR (400 MHz, CDCl3) δ 7.49− 7.35 (m, 2H, Ar), 6.91−6.86 (m, 2H, Ar), 4.85−4.73 (2H, NH2), 4.70−4.68 (m, 2H, NCH2N), 4.51−4.29 (m, 4H, NCH2N), 4.14− 4.07 (m, 2H, NCH2N), 3.88−3.73 (m, 6H, 3 NCH2N, 3 CH3), 3.67− 3.58 (m, 4H, PCH2N). 13C{1H} NMR (100 MHz, CDCl3) δ 160.7 (s, C11, E), 160.1 (s, C11, Z), 154.6 (d, 1JPC = 11.8 Hz, C1, Z), 153.3 (d, 1 JPC = 19.3 Hz, C1, E) 130.3 (d, 4JPC = 0.9 Hz, C9,13 Z), 128.1 (s, C9,13, E), 128.1 (d, 3JPC = 11.3 Hz, C8, Z), 126.3 (d, 3JPC = 2.7 Hz, C8, E), 113.4 (s, C10,12, Z), 113.1 (s, C10,12, E), 110.9 (d, 2JPC = 104.7 Hz, C7, E), 108.5 (d, 2JPC = 91.9 Hz, C7, Z), 74.5 (d, 3JPC = 8.1 2
H
DOI: 10.1021/acs.inorgchem.8b01167 Inorg. Chem. XXXX, XXX, XXX−XXX
Inorganic Chemistry
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NMR (162 MHz, CD2Cl2) −37.4 (1JPW = 210.6 Hz). Solid state IR (cm−1): υ(NH) 3330; υ(CO) 2013, 1908, 1869, 1814. Synthesis of W(CO)4PTA-C(C6H5OMe)NH, 11. To a 50 mL Schlenk flask containing W(CO)4(pip)2 (0.33 g, 0.71 mmol) and 3 (0.21 g, 0.71 mmol) was added 30 mL of degassed toluene via cannula resulting in a yellow suspension. The suspension was heated to 65 °C for 36 h under nitrogen. The resulting reddish brown solution was filtered through Celite and the solvent removed under vacuum with the resulting reddish brown solid dissolved in 2 mL of dichloromethane and precipitated with hexanes (∼20 mL). Upon filtration, 0.27 g (0.46 mmol, 64% yield) of 11 was obtained as a bright yellow powder. 1H NMR (400 MHz, CD2Cl2) δ 9.79 (d, 3JPH = 7.9 Hz, 1H, NH), 7.57 (d, J = 8.9 Hz, 2H, ArH), 6.88 (d, J = 6.8 Hz, 2H, ArH), 4.81 (s, 1H, PCHN), 4.76−4.61 (dd, J = 13.6, 2.1 Hz, 1H, NCH2N), 4.48 (m, 1H, NCH2N), 4.42−4.38 (m, 2H, NCH2N), 4.20−4.07 (m, 1H NCH2N; 2H PCH2N), 3.78 (s, 3H, OCH3), 3.71− 3.59 (m, 2H, PCH2N). 13C{1H} NMR (100 MHz, CDCl3) δ 212.2 (d, 2JPC = 4.1 Hz, C2), 209.7 (d, 2JPC = 34.2 Hz, C1), 202.3 (d, 2JPC = 8.5 Hz, C3), 202.0 (d, 2JPC = 5.3 Hz, C4), 183.6 (d, 2JPC = 7.1 Hz, C11), 162.8 (s, C15), 129.0 (d, 4JPC = 15.3 Hz, C13,17), 126.5 (d, 3 JPC = 3.3 Hz, C12), 114.0 (s, C14,16), 75.1 (d, 3JPC = 3.3 Hz, C9), 72.4 (d, 3JPC = 6.8 Hz, C8), 70.5 (d, 1JPC = 16.5 Hz, C5), 68.9 (d, 3JPC = 6.8 Hz, C10), 55.5 (s, C18), 53.8 (d, 1JPC = 2.9 Hz, C6), 53.7 (d, 1 JPC = 3.8 Hz, C7). 31P{1H} NMR (162 MHz, CD2Cl2) −38.7 (1JPW = 217.4 Hz). Solid state IR (cm−1) υ(NH) 3256; υ(CO) 2005, 1862, 1849, 1820. HRMS (ESI, CH3OH) m/z for C18H20N4O5PW [M + H+]: calcd 587.0681; found 587.0672. Synthesis of W(CO)4(pip)PTAC(C6H5OMe)NH2, 11a. To a suspension of W(CO)4(pip)2 (0.16 g, 0.34 mmol) in 20 mL of degassed dichloromethane was added a solution of 3 (0.10 g, 0.34 mmol) in 20 mL of degassed dichloromethane slowly via cannula. The resulting yellow suspension was stirred under nitrogen at room temperature for 1 h providing a wine red solution. The solution was filtered through Celite and the solvent removed under vacuum. The residual reddish brown solid was dissolved in 2 mL of dichloromethane and precipitated with hexanes (∼20 mL) resulting in the isolation of 0.11 g (∼22% yield) of a bright yellow powder with 11b as the major component of a mixture of 11a, 11b, and 11. 31P{1H} NMR (162 MHz, CDCl3) −67.7 (1JPW = 215.0 Hz). X-ray quality crystals of 11b were grown by slow diffusion of hexane into a dichloromethane solution of the mixture at room temperature. Synthesis of W(CO)4PTA-C(C6H5(OMe)3)NH), 12. To a 50 mL Schlenk flask containing W(CO)4(pip)2 (0.42 g, 0.90 mmol) and 4 (0.22 g, 0.90 mmol) was added 30 mL of degassed toluene via cannula resulting in a yellow suspension. The suspension was heated to 65 °C for 20 h under nitrogen. The resulting reddish brown suspension was filtered providing 12 as a dark yellow solid (0.34 g, 0.53 mmol, 58% yield). 1H NMR (500 MHz, CD2Cl2): δ 10.02 (d, 3 JPH = 7.9 Hz, 1H, NH), 6.89 (s, 2H, Ar), 4.94 (s, 1H PCHN), 4.80 (dd, J = 71.8, 13.4 Hz, 2H, NCH2N), 4.59 (dd, J = 15.3, 4.4 Hz, 1H, NCH2N), 4.51 (q, J = 13.8 Hz, 2H, NCH2N), 4.30−4.22 (m, 1H, NCH2N; 2H PCH2N), 3.89 (s, 6H, OCH3), 3.86 (s, 3H, OCH3), 3.82−3.72 (m, 2H, PCH2N). 13C{1H} NMR (100 MHz, CD2Cl2) δ 212.1 (d, 2JPC = 4.2 Hz, C2), 209.6 (d, 2JPC = 34.2 Hz, C1), 202.4 (d, 2 JPC = 8.5 Hz, C3), 202.0 (d, 2JPC = 5.4 Hz, C4), 184.1 (d, 2JPC = 7.2 Hz, C11), 153.4 (s, C14,16), 141.7 (s, C15), 129.0 (d, 3JPC = 3.4 Hz, C12), 104.8 (s, C13,17), 75.0 (d, 3JPC = 3.3 Hz, C9), 72.4 (d, 3JPC = 6.8 Hz, C8), 70.9 (d, 1JPC = 16.4 Hz, C5), 69.1 (d, 3JPC = 6.7 Hz, C10), 60.6 (s, C19), 56.4 (s, C18, 20), 53.8 (d, 2JPC = 2.5 Hz, C6), 53.7 (d, 2JPC = 3.3 Hz, C7). 31P{1H} NMR (162 MHz, CD2Cl2) −38.1 (1JPW = 217.5 Hz). Solid state IR (cm−1): υ(NH) 3215; υ(CO) 2012, 1917, 1883, 1858. HRMS (ESI, CH 3 OH) m/z for C20H24N4O7PW [M + H+]: calcd 647.0892; found 647.0879. X-ray quality crystals were grown by slow evaporation of a 1:1 dichloromethane/hexane solution of 12 in a freezer over the course of a few weeks.
Article
ASSOCIATED CONTENT
S Supporting Information *
The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acs.inorgchem.8b01167. IR, NMR, MS, and X-ray data for many of the compounds (PDF) Accession Codes
CCDC 1837955−1837960 contain the supplementary crystallographic data for this paper. These data can be obtained free of charge via www.ccdc.cam.ac.uk/data_request/cif, or by emailing
[email protected], or by contacting The Cambridge Crystallographic Data Centre, 12 Union Road, Cambridge CB2 1EZ, UK; fax: +44 1223 336033.
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AUTHOR INFORMATION
Corresponding Author
*E-mail:
[email protected]. ORCID
Brian J. Frost: 0000-0002-0127-9635 Notes
The authors declare no competing financial interest.
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ACKNOWLEDGMENTS The authors thank Donald Krogstad for helpful discussions and assistance and Juan Carlos Chavez for help with experiments, the National Science Foundation (CHE0645365) and the donors of the American Chemical Society Petroleum Research Fund (PRF 43574-G3) supported parts of this work. The NSF-REU program (CHE-0552816) is gratefully acknowledged for summer support (T.L.S.).
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REFERENCES
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DOI: 10.1021/acs.inorgchem.8b01167 Inorg. Chem. XXXX, XXX, XXX−XXX
Article
Inorganic Chemistry
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DOI: 10.1021/acs.inorgchem.8b01167 Inorg. Chem. XXXX, XXX, XXX−XXX
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DOI: 10.1021/acs.inorgchem.8b01167 Inorg. Chem. XXXX, XXX, XXX−XXX
