Complexes of Technetium(V) and Rhenium(V) with β-Diketonates

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Cite This: Inorg. Chem. XXXX, XXX, XXX−XXX

Complexes of Technetium(V) and Rhenium(V) with β‑Diketonates Clemens Scholtysik, Christelle Njiki Noufele, Adelheid Hagenbach, and Ulrich Abram* Freie Universität Berlin, Institute of Chemistry and Biochemistry, Fabeckstrasse 34/36, D-14195 Berlin, Germany

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ABSTRACT: Reactions of (NBu4)[MOCl4] complexes (M = Tc or Re) with an excess of hexafluoroacetylacetone (Hhfac) give products with a composition of (NBu4)[MOCl3(hfac)] as bright yellow (Tc) or red (Re) solids. The products are stable as solids but rapidly decompose in solution. A number of related phenylimidorhenium(V) complexes were synthesized starting from [Re(NPhF)Cl3(PPh3)2], where (NPhF)2− is a para-fluorinated phenylimido ligand. Products with compositions of [Re(NPhF)Cl2(PPh3)(acac)], [Re(NPhF)Cl2(PPh3)(hfac)], [Re(NPhF)Cl2(PPh3)(tfac)], [Re(NPhF)Cl2(PPh3)(naphtfac)], and [Re(NPhF)Cl2(PPh3)(tbutfac)] (Hacac = acetylacetone, Htfac = trifluoroacetylacetone, Hnaphtfac = naphthoyltrifluoroacetylmethane, and Htbutfac = tert-butyroyltrifluoroacetylmethane) were isolated from reactions of the quite soluble [Re(NPhF)Cl3(PPh3)2] with the corresponding β-diketones and studied spectroscopically and by X-ray diffraction. The β-diketonates are coordinated in a meridional arrangement with the phenylimide. The formation of two isomers was detected for nonsymmetric β-diketones with a preference for the “equatorial” position for the more bulky substituents. Products with more than one chelating ligand were not obtained. The technetium complexes [Tc(NPhX)Cl3(PPh3)2] (X = p-F or p-CF3) were prepared from reactions of pertechnetate, PPh3, HCl, and substituted arylacetylhydrazines and isolated as green solids. They are sufficiently stable as solid but rapidly decompose in moist solvents upon hydrolysis of the Tc−N bonds. From reactions of [Tc(NPh)Cl3(PPh3)2] or [Tc(NPhF)Cl3(PPh3)2] in dry solvents, the complexes [Tc(NPh)Cl2(PPh3)(hfac)] and [Tc(NPhF)Cl2(PPh3)(hfac)] were prepared and isolated in crystalline form. An X-ray diffraction study shows that fluorination of the para position of the phenylimido ligand results in a slight lengthening of all bonds in the coordination sphere of technetium.

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INTRODUCTION Acetylacetonates (acac−) and their derivatives belong to the most widely used ligand systems for the complexation of metal ions. More than 12000 such compounds have been studied crystallographically, and acetylacetonato complexes of almost all transition metals are well-known.1 Thus, it is surprising that so far only three technetium complexes with acetylacetonates have been studied by X-ray diffraction.2−4 They are shown in Chart 1. Additionally, a small series of technetium(III) and technetium(IV) complexes has been prepared from ligand exchange reactions starting from [TcX4(PPh3)2] (X = Cl or Br) complexes or pertechnetate.5,6 Technetium complexes with substituted acetylacetonates have been hitherto unknown. The chemistry of rhenium acetylacetonates is more diverse, and with the heavier congener of technetium, complexes with the transition metal in lower oxidation states dominate.1 In particular, tricarbonylrhenium(I) complexes with one acetylacetonato and an additional monodentate ligand have recently aroused interest.7−11 Rhenium acetylacetonates and related compounds with the metal in its higher oxidation states are rare, and only a few oxidorhenium(V) compounds have been isolated and structurally characterized.12−16 Compounds with nitrido or phenylimido co-ligands have not yet been © XXXX American Chemical Society

considered. One of the reasons for this surprising lack of knowledge may be the absence of suitable starting materials. Common compounds such as [MNCl2(PPh3)2] or [M(NPh)Cl3(PPh3)2] (M = Tc or Re) are only sparingly soluble. The reaction of acetylacetone with [ReOCl2(OEt)(PPh3)2] (the corresponding Tc compounds [TcOCl2(OEt)(PPh3)2] and [TcOCl3(PPh3)2] do not exist) gave only small amounts of [ReOCl2(acac)(PPh3)] and a corresponding diffraction study was performed on some “hand-picked” crystals.16 Thus, the only reliably synthesized oxidorhenium(V) complexes seem to be (NBu4)[ReOCl3(L)], where HL is acetylacetone, benzoylacetone, or dibenzoylmethane. They are generated in good yields from reactions between (NBu4)[ReOCl4] and the respective diketones.13 This surprising lack of knowledge encouraged us to undertake some more studies with rhenium and technetium compounds. These two central elements of the periodic table of elements can stabilize complexes with a large number of oxidation states, and deeper insight into their chemistry with such fundamental ligands like β-diketones is of general interest. Received: February 3, 2019

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DOI: 10.1021/acs.inorgchem.9b00326 Inorg. Chem. XXXX, XXX, XXX−XXX

Article

Inorganic Chemistry Chart 1. Structurally Characterized Technetium Complexes with Acetylacetonate

4C, CH3). IR (KBr): 2968 (s), 2939 (m), 2879 (m), 1599 (s), 1555 (s), 1483 (s), 1447 (s), 1383 (m), 1356 (m), 1261 (s), 1225 (s), 1146 (s), 1111 (s), 991 (s), 893 (m), 802 (s), 745 (m), 667 (s), 608 (w), 588 (w), 530 (w), 509 (w), 478 (w) cm−1. ESI-MS: m/z 514.8589 [M]− (calcd 514.8453). (NBu4)[TcOCl3(hfac)]. (NBu4)[TcOCl4] (118 mg, 0.2 mmol) was dissolved in 5 mL of dry, argon-purged CH2Cl2, and Hhfac (0.15 mL, ∼1 mmol) was added. The color of the solution changed immediately to bright yellow. The solvent was removed in vacuum, and the resulting bright yellow solid was washed twice with 5 mL of water and dried in air. Yield: 130 mg (86%). Elemental Anal. Calcd for C19H36NO3Cl3Tc: Tc, 14.9%. Found: Tc, 14.8%. 1H NMR (CDCl3): δ 6.02 (s, 1H, CH), 3.19 (s, 2H, CH2), 1.65 (s, 2H, CH2), 1.42 (s, 2H, CH2), 0.98 (s, 3H, CH3). 19F NMR (CDCl3): δ −74.1 (s, 3F, CF3), −75.5 (s, 3F, CF3). IR (KBr): 3363 (w), 3271 (w), 3134 (w), 2964 (s), 2943 (s), 2875 (s), 2031 (w), 1934 (w), 1722 (w), 1643 (s), 1555 (m), 1514 (w), 1469 (s), 1383 (m), 1354 (m), 1257 (s), 1211 (s), 1147 (s), 1109 (s), 1066 (w), 1024 (s), 988 (s), 883 (m), 797 (m), 736 (m), 667 (s), 599 (w), 588 (w), 532 (w), 507 (w) cm−1. [Tc(NPhF)Cl3(PPh3)2]. NH4TcO4 (180 mg, 1 mmol) was dissolved in 70 mL of MeOH. PPh3 (1.310 g, 5 mmol) and N′-4fluorophenylacetohydrazide (185 mg, 1.1 mmol) were dissolved in 35 mL of MeOH each and added to the mixture. The solution was heated under reflux for 20 min. After the mixture had cooled to room temperature, HCl (35%, 1.5 mL) was added dropwise and the mixture was stirred for 15 min at room temperature. The resulting dark green solid was filtered off, washed with MeOH and n-hexane, and dried in air. Yield: 459 mg (55%). Elemental Anal. Calcd for C42H34NP2Cl3FTc: Tc, 11.8%. Found: Tc, 12.2%. 1H NMR (CD2Cl2): δ 7.79−7.81 (m, 12H, HaromPPh3), 7.21−7.31 (m, 18H, HaromPPh3), 7.08−7.11 (m, 2H, HaromNPhF), 6.40−6.44 (t, J = 8.0 Hz, 2H, HaromNPhF). 19F NMR (CD2Cl2): δ −97.9 (s). IR (KBr): 3059 (w), 1578 (w), 1481 (m), 1433 (s), 1337 (w), 1315 (w), 1234 (w), 1188 (w), 1161 (w), 1144 (w), 1090 (m), 1072 (w), 1028 (w), 997 (w), 845 (w), 743 (s), 692 (s), 520 (s), 509 (m), 492 (m) 449 (w) cm−1. [Tc(NPhCF3)Cl3(PPh3)2]. NH4TcO4 (72 mg, 0.4 mmol) was dissolved in 40 mL of MeOH. PPh3 (524 mg, 2 mmol) and N′-4trifluoromethylphenylacetohydrazide (96 mg, 0.44 mmol) were dissolved in 10 mL of MeOH each and added to the mixture. The solution was heated under reflux for 20 min. After the mixture had been cooled to room temperature, HCl (35%, 0.75 mL) was added dropwise and the mixture was stirred for 15 min at room temperature. The resulting dark green solid was filtered off, washed with MeOH and n-hexane, and dried in air. Yield: 110 mg (25%). Elemental Anal. Calcd for C43H34NP2Cl3F3Tc: Tc, 11.1%. Found: Tc, 11.8%. 1H NMR (CD2Cl2): δ 7.79−7.83 (m, 12H, HaromPPh3), 7.20−7.30 (m, 18H, HaromPPh3), 7.13−7.16 (m, 2H, HaromNPhF), 6.96 (t, J = 8.0 Hz, 2H, HaromNPhF). 19F NMR (CD2Cl2): δ −63.9 (s). IR (KBr): 3057 (m), 2918 (w), 1591 (w), 1570 (w), 1481 (s), 1433 (s), 1321 (s), 1180 (m), 1128 (s), 1092 (s), 1064 (m), 1028 (w), 1001 (m), 925 (w), 849 (m), 746 (s), 692 (s), 599 (w), 517 (s), 449 (m) cm−1. [Tc(NPh)Cl2(PPh3)(hfac)]. [Tc(NPh)Cl3(PPh3)2] (82 mg, 0.1 mmol) was suspended in 5 mL of toluene, and Hhfac (0.07 mL, ∼0.4 mmol) was added. The mixture was heated under reflux for 3.5 h and then filtered. The product crystallized from the filtrate by slow

Particularly interesting are compounds of medium oxidation states, which are frequently formed by reduction of pertechnetate or perrhenate with common reductants in aqueous media, conditions that are relevant for the production of 99mTc or 186,188Re radiopharmaceuticals.17,18 Recently, we reported the synthesis of the fluorinated phenylimido complex [Re(NPhF)Cl3(PPh3)2].19 This compound shows a solubility considerably higher than that of [Re(NPh)Cl3(PPh3)2] and might be a good candidate for controlled ligand exchange reactions. In this study, we extend the chemistry of fluorinated phenylimido ligands to technetium and describe the syntheses, structures, and spectroscopic behavior of some {M(NPhF)}3+ (M = Re or Tc) complexes with fluorinated β-diketonato ligands.

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EXPERIMENTAL SECTION

Materials. All chemicals used in this study were reagent grade and used without further purification. Dry toluene was obtained from an MBraun SPS-800 solvent drying device. The following compounds were synthesized according to literature procedures: (NBu4)[ReOCl4],20 (NBu4)[TcOCl4],21 [Re(NPhF)Cl3(PPh3)2],19 [Tc(NPh)Cl3(PPh3)2],22 N′-4-fluorophenylacetohydrazide,23 and N′-4trifluoromethylphenylacetohydrazide.23 Physical Measurements. Infrared (IR) spectra were recorded from KBr pellets on a Shimadzu FTIR 8300 spectrometer (Tc complexes) or on a Thermo Scientific Nicolet iS10 ATR spectrometer (all other compounds). Nuclear magnetic resonance (NMR) spectra were recorded on a JEOL 400 MHz spectrometer. ESI mass spectra were measured with an Agilent 6210 ESI-TOF instrument (Agilent Technology). Elemental analysis of carbon, hydrogen, nitrogen, and sulfur was performed using a Heraeus vario EL elemental analyzer. The technetium contents were detemined with a HIDEX 300 SL scintillation counter. Density functional theory (DFT) calculations were done with Gaussian 09 (G09), considering different DFT levels (B3LYP and PBE1PBE).24−27 The initial geometry for the optimization of the structures was taken from the data of the crystal structure analysis of [Re(NPhF)Cl2(PPh3)(tfac)]. The quasirelativistic pseudopotentials and the corresponding optimized basis sets Stuttgart ECP 1997 and LANL2DZ were used for rhenium.28,29 The basis sets 6-31G* and 6311++G** were used for all other atoms. Syntheses of the Complexes. (NBu4)[ReOCl3(hfac)]. (NBu4)[ReOCl4] (118 mg, 0.2 mmol) was dissolved in 5 mL of dry, argonpurged CH2Cl2, and hexafluoroacetylacetone (Hhfac) (0.15 mL, ∼1 mmol) was added. The color of the mixture changed immediately to deep red. The solvent was removed in vacuum, and the obtained red solid was washed twice with 5 mL of H2O and dried in air. Yield: 130 mg (86%). Elemental Anal. Calcd for C19H36NO3Cl3Re: C, 34.1%; H, 5.3%; N, 1.7%. Found: C, 33.3%; H, 4.9%; N, 1.8%. 1H NMR (CDCl3): δ 6.34 (s, 1H, CH), 3.18 (dd, 2H, CH2), 1.62 (dd, 2H, CH2), 1.41 (dd, 2H, CH2), 0.99 (t, 3H, CH3). 19F NMR (CDCl3): δ −72.3 (s, 3F, CF3), −73.7 (s, 3F, CF3). 13C NMR (CDCl3): δ 182.8 (d, J = 37 Hz, 1C, CO), 179.3 (d, J = 37 Hz, 1C, CO), 114.2 (q, J = 280 Hz, 1C, CF3), 113.7 (q, J = 280 Hz, 1C, CF3), 84.5 (s, 1C, CH), 60 (s, 4C, CH2), 24.4 (s, 4C, CH2), 20 (s, 4C, CH2), 13.8 (s, B

DOI: 10.1021/acs.inorgchem.9b00326 Inorg. Chem. XXXX, XXX, XXX−XXX

Article

Inorganic Chemistry

6.70 (s, 1H, CH). 19F NMR (CDCl3): δ −72,9 (s, 3F, CF3), −73,8 (s, 3F, CF3), −101.9 (ttd, J = 7.5 Hz, J = 3.8 Hz, J = 1.1 Hz, 1F, NPhF). 31 P NMR (CDCl3): δ −0.4 (s). 13C NMR (CDCl3): δ 177.8 (d, J = 40 Hz, 1C, CO), 175.6 (d, J = 40 Hz, 1C, CO), 161.9 (d, J = 258 Hz, 1C, CaromNPhF), 153.2 (s, 1C, CaromNPhF), 134.7 (d, J = 9 Hz, 6C, CaromPPh3), 131.3 (d, J = 2 Hz, 6C, CaromPPh3), 130 (d, J = 58 Hz, 3C, CaromPPh3), 128.3 (d, J = 11 Hz, 6C, CaromPPh3), 125.9 (dd, J = 10 Hz, 2C, CaromNPhF), 117 (d, J = 20 Hz, 2C, CaromNPhF), 115.8 (q, J = 280 Hz, 1C, CF3), 115.7 (q, J = 280 Hz, 1C, CF3), 89.9 (s, 1C, CH). IR (KBr): 3063 (w), 1587 (s), 1554 (m), 1483 (m), 1445 (s), 1436 (s), 1363 (w), 1350 (m), 1291 (w), 1258 (s), 1242 (m), 1199 (s), 1165 (w), 1146 (s), 1108 (m), 1092 (s), 1027 (w), 1016 (w), 998 (w), 950 (w), 842 (s), 818 (w), 802 (s), 746 (s), 709 (m), 693 (s), 669 (s), 599 (m), 561 (m), 549 (w), 529 (s) cm−1. ESI+ MS (m/ z): 857.9974 [M + Na]+ (calcd 857.9952), 873.9714 [M + K]+ (calcd 873.9692). [Re(NPhF)Cl2(PPh3)(tfac)]. [Re(NPhF)Cl3(PPh3)2] (186 mg, 0.2 mmol) was suspended in 5 mL of toluene. Trifluoroacetylacetone (Htfac) (0.1 mL, ∼0.8 mmol) was added, and the mixture was heated under reflux for 4 h. After the solvent had been removed under vacuum, the residue was washed with n-hexane, yielding the product as a dark green powder. Crystals suitable for X-ray diffraction were obtained by slow evaporation of a CH2Cl2/MeOH/MeCN solution at −20 °C. Yield: 107 mg (70%). Elemental Anal. Calcd for C29H23NO2PCl2F4Re: C, 44.6%; H, 3.0%; N, 1.8%. Found: C, 44.6%; H, 3.0%; N, 1.7%. 1H NMR (CDCl3): δ 7.63−7.72 (m, 12H, HaromPPh3), 7.33−7.44 (m, 18H, HaromPPh3), 7.23−7.28 (m, 4H, HaromNPhF), 6.81−6.87 (m, 4H, HaromNPhF), 6,41 (s, 1H, CH), 6,20 (s, 1H, CH), 3.20 (s, 3H, CH3), 2.14 (s, 3H, CH3). 19F NMR (CDCl3): δ −72.8 (s, 3F, CF3), −73.6 (s, 3F, CF3), −103.8 (ttd, J = 7.5 Hz, J = 3.8 Hz, J = 1.1 Hz, 1F, PhF), −103.9 (ttd, J = 7.5 Hz, J = 3.8 Hz, J = 1.1 Hz, 1F, PhF). 31P NMR (CDCl3): δ −0,5 (s), −4.2 (s). 13C NMR (CDCl3): δ 198 (s, 1C, CO), 196.3 (s, 1C, CO), 170.7 (d, J = 37 Hz, 1C, CO), 167.1 (d, J = 34 Hz, 1C, CO), 161.3 (d, J = 255 Hz, 1C, CaromNPhF), 161.2 (d, J = 255 Hz, 1C, CaromNPhF), 153.6 (s, 1C, CaromNPhF), 153.4 (s, 1C, CaromNPhF), 134.7 (d, J = 9 Hz, 6C, CaromPPh3), 134.6 (d, J = 9 Hz, 6C, CaromPPh3), 131.4 (d, J = 57 Hz, 3C, CaromPPh3), 131.1 (d, J = 57 Hz, 3C, CaromPPh3), 131.1 (d, J = 3 Hz, 3C, CaromPPh3), 130.9 (d, J = 3 Hz, 3C, CaromPPh3), 128.1 (d, J = 11 Hz, 6C, CaromPPh3), 127.9 (d, J = 11 Hz, 6C, CaromPPh3), 125.1 (d, J = 10 Hz, 2C, CaromNPhF), 125.1 (d, J = 10 Hz, 2C, CaromNPhF), 117.3 (q, J = 280 Hz, 1C, CF3), 116.7 (d, J = 24 Hz, 2C, CaromNPhF), 116.7 (d, J = 24 Hz, 2C, CaromNPhF), 96.2 (q, J = 3 Hz, 1C, CH), 94.7 (q, J = 3 Hz, 1C, CH), 28.6 (d, J = 3 Hz, 1C, CH3), 25.7 (s, 1C, CH3). IR (KBr): 3062 (w), 1611 (m), 1584 (s), 1525 (m), 1482 (s), 1435 (s), 1362 (m), 1294 (s), 1227 (s), 1194 (m), 1167 (w), 1134 (s), 1092 (s), 1027 (w), 1015 (w), 999 (w), 869 (w), 841 (s), 817 (w), 797 (m), 747 (s), 731 (m), 708 (w), 692 (s), 613 (w), 586 (m), 562 (m), 529 (s) cm−1. ESI+ MS (m/z): 518.9446 [M − PPh3]+ (calcd 518.9425), 592.0427 [M − tfac − Cl − H]+ (calcd 592.0407), 628.0189 [M − tfac]+ (calcd 628.0174), 672.0022 [M − NPhF]+ (calcd 672.0010), 710.0926 [M − 2Cl − H]+ (calcd 710.0882), 746.0666 [M − Cl]+ (calcd 746.0649), 781.0358 [M]+ (calcd 781.0337), 804.0249 [M + Na]+ (calcd 804.0235), 819.9986 [M + K]+ (calcd 819.9974). [Re(NPhF)Cl2(PPh3)(naphtfac)]. [Re(NPhF)Cl3(PPh3)2] (186 mg, 0.2 mmol) was suspended in 5 mL of toluene. Naphthoyltrifluoroacetylmethane (Hnaphtfac) (213 mg, 0.8 mmol) was added, and the mixture was heated under reflux for 6 h. After the solvent had been removed under vacuum, the residue was washed with MeOH and nhexane. The residue was extracted with MeCN; unreacted starting material was filtered off, and the solvent was removed under vacuum. The product was obtained as a dark green powder. Yield: 81 mg (45%). Elemental Anal. Calcd for C38H30NO2PCl2F4Re: C, 51.1%; H, 3.0%; N, 1.6%. Found: C, 51.0%; H, 3.2%; N, 1.5%. 1H NMR (CDCl3): δ 8.41 (s, 1H, CH), 8.01−8.03 (m, 1H, Harom), 7.86−7.93 (m, 3H, Harom), 7.69−7.77 (m, 9H, Harom), 7.51−7.59 (m, 3H, Harom), 7.27−7.50 (m, 14H, Harom), 7.22 (s, 1H, CH), 6.85−6.89 (m, 2H, HaromNPhF). 19F NMR (CDCl3): δ −72.3 (s, 3F, CF3), −73.2 (s, 3F, CF3), −103.6 (ttd, J = 8.1 Hz, J = 5.0 Hz, J = 1.5 Hz, 1F, PhF),

evaporation of the solvent as dark green crystals, which were suitable for X-ray diffraction. Yield: 23 mg (31%). Elemental Anal. Calcd for C29H21NO2PCl2F6Tc: Tc, 13.6%. Found: Tc, 12.2%. 1H NMR (CD2Cl2): δ 7.72 (t, J = 8 Hz, 1H, HaromNPh), 7.62−7.67 (m, 8H, HaromPPh3/NPh), 7.46−7.50 (m, 3H, HaromPPh3), 7.35−7.40 (m, 6H, HaromPPh3), 7.21 (t, J = 8.0 Hz, 2H, HaromNPhF), 6.41 (s, 1H, CH). 19 F NMR (CD2Cl2): δ −74.8 (s), −75 (s). IR (KBr): 3140 (w), 3057 (m), 2989 (w), 2960 (w), 2924 (w), 1969 (w), 1899 (w), 1822 (w), 1625 (s), 1589 (s), 1575 (s), 1556 (s), 1519 (w), 1483 (s), 1456 (m), 1436 (s), 1392 (w), 1350 (w), 1330 (m), 1313 (m), 1259 (s), 1205 (s), 1151 (s), 1118 (s), 1089 (s), 1076 (s), 1026 (s), 997 (s), 941 (s), 925 (w), 850 (w), 798 (m), 748 (s), 725 (s), 692 (s), 671 (s), 617 (w), 596 (w), 536 (s), 511 (m), 453 (w), 443 (w), 422 (w) cm−1. [Tc(NPhF)Cl2(PPh3)(hfac)]. [Tc(NPhF)Cl3(PPh3)2] (84 mg, 0.1 mmol) was suspended in 5 mL of dry toluene under an argon atmosphere. Hhfac (0.07 mL, ∼0.4 mmol) was added, and the mixture was heated under reflux for 4 h. After the solvent had been removed under vacuum, the residue was dissolved in 1.0 mL of CH2Cl2 and a dark green solid precipitated after the addition of 7 mL of n-hexane. Crystals suitable for X-ray diffraction were obtained by slow evaporation of a solution in MeCN at −20 °C. Yield: 34 mg (45%). Elemental Anal. Calcd for C29H20NO2PCl2F7Tc: Tc, 13.2%. Found: Tc, 12.4%. 1H NMR (CD2Cl2): δ 7.67−7.71 (m, 2H, HaromNPhF), 7.61−7.66 (m, 6H, HaromPPh3), 7.47−7.49 (m, 3H, HaromPPh3), 7.36−7.40 (m, 6H, HaromPPh3), 6.86−6.90 (m, 2H, HaromNPhF), 6.42 (s, 1H, CH). 19F NMR (CD2Cl2): δ −74.8 (s, 3F, CF3), −75.0 (s, 3F, CF3), −95.1 (s, 1F, NPhF). IR (KBr): 3059 (m), 1587 (m), 1571 (m), 1481 (s), 1433 (s), 1394 (w), 1328 (w), 1313 (m), 1259 (m), 1188 (m), 1153 (s), 1122 (s), 1089 (s), 1028 (m), 997 (m), 974 (w), 927 (w), 842 (w), 804 (w), 742 (s), 727 (m), 690 (s), 619 (w), 534 (m), 518 (s), 505 (s), 491 (s), 447 (m), 428 (w) cm−1. [Re(NPhF)Cl2(PPh3)(acac)]. [Re(NPhF)Cl3(PPh3)2] (186 mg, 0.2 mmol) was suspended in 5 mL of toluene. Acetylacetone (0.08 mL, ∼0.8 mmol) was added, and the mixture was heated under reflux for 4 h. After the solvent had been removed under vacuum, the residue was washed with n-hexane, yielding the product as a light green powder. Crystals suitable for X-ray diffraction were obtained by slow evaporation of a CH2Cl2/MeOH solution. Yield: 109 mg (75%). Elemental Anal. Calcd for C29H26NO2PCl2FRe: C, 47.9%; H, 3.6%; N, 1.9%. Found: C, 47.7%; H, 3.8%; N, 1.9%. 1H NMR (CDCl3): δ 7.67−7.72 (m, 6H, HaromPPh3), 7.33−7.41 (m, 9H, HaromPPh3), 7.23−7.27 (m, 2H, HaromNPhF), 6.78−6.83 (m, 2H, HaromNPhF), 5.94 (s, 1H, CH), 2.91 (s, 3H, CH3), 1.94 (s, 3H, CH3). 19F NMR (CDCl3): δ −105.6 (ttd, J = 7.5 Hz, J = 3.8 Hz, J = 1.1 Hz). 31P NMR (CDCl3): δ −3.4 (s). 13C NMR (CDCl3): δ 191.4 (d, J = 2 Hz, 1C, CO), 186.6 (d, J = 2 Hz, 1C, CO), 161.1 (d, J = 254 Hz, 1C, CaromNPhF), 153.8 (s, 1C, CaromNPhF), 134.9 (d, J = 9 Hz, 6C, CaromPPh3), 132.3 (d, J = 55 Hz, 3C, CaromPPh3), 130.8 (d, J = 3 Hz, 3C, CaromPPh3), 128 (d, J = 11 Hz, 6C, CaromPPh3), 125.2 (dd, J = 20 Hz, J = 2 Hz, 2C, CaromNPhF), 116.3 (d, J = 24 Hz, 2C, CaromNPhF), 100.2 (s, 1C, CH), 27.9 (d, J = 3 Hz, 1C, CH3), 24.7 (s, 1C, CH3). IR (KBr): 3059 (m), 1587 (m), 1571 (m), 1481 (s), 1433 (s), 1394 (w), 1328 (w), 1313 (m), 1259 (m), 1188 (m), 1153 (s), 1122 (s), 1089 (s), 1028 (m), 997 (m), 974 (w), 927 (w), 842 (w), 804 (w), 742 (s), 727 (m), 690 (s), 619 (w), 534 (m), 518 (s), 505 (s), 491 (s), 447 (m), 428 (w) cm−1. ESI+ MS (m/z): 692.0965 [M − Cl]+ (calcd 692.0931), 750.0544 [M + Na]+ (calcd 750.0518), 766.0283 [M + K]+ (calcd 766.0257). [Re(NPhF)Cl2(PPh3)(hfac)]. [Re(NPhF)Cl3(PPh3)2] (186 mg, 0.2 mmol) was suspended in 5 mL of toluene. Hhfac (0.13 mL, ∼0.8 mmol) was added, and the mixture was heated under reflux for 3.5 h. After the solvent had been removed under vacuum, the residue was washed with n-hexane, yielding the product as a dark green powder. Crystals suitable for X-ray diffraction were obtained by slow evaporation of a CH2Cl2/MeOH solution. Yield: 135 mg (80%). Elemental Anal. Calcd for C29H20NO2PCl2F7Re: C, 41.7%; H, 2.4%; N, 1.7%. Found: C, 41.6%; H, 2.9%; N, 1.5%. 1H NMR (CDCl3): δ 7.63−7.68 (m, 6H, HaromPPh3), 7.37−7.45 (m, 9H, HaromPPh3), 7.24−7.28 (m, 2H, HaromNPhF), 6.86−6.90 (m, 2H, HaromNPhF), C

DOI: 10.1021/acs.inorgchem.9b00326 Inorg. Chem. XXXX, XXX, XXX−XXX

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Inorganic Chemistry −103.9 (ttd, J = 8.1 Hz, J = 5.0 Hz, J = 1.5 Hz, 1F, PhF). 31P NMR (CDCl3): δ −2.7 (s), −3.2 (s). 13C NMR (CDCl3): δ 188.6 (s, 1C, CO), 187.9 (s, 1C, CO), 168.3 (d, J = 35 Hz, 1C, CO), 161.5 (d, J = 256 Hz, 1C, CaromNPhF), 153.5 (s, 1C, CaromNPhF), 136.2 (s, 1C, Carom), 135.8 (s, 1C, Carom), 134.8 (d, J = 9 Hz, 6C, CaromPPh3), 134.7 (d, J = 9 Hz, 6C, CaromPPh3), 132.3 (s, 1C, Carom), 132.3 (s, 1C, Carom), 131.7 (s, 1C, Carom), 131.6 (s, 1C, Carom), 131.5 (d, J = 57 Hz, 3C, CaromPPh3), 131.2 (s, 1C, Carom), 131.1 (s, 1C, Carom), 131 (d, J = 57 Hz, 3C, CaromPPh3), 131 (s, 3C, CaromPPh3), 130.8 (s, 1C, Carom), 130.9 (s, 3C, CaromPPh3), 130 (s, 1C, Carom), 129.9 (s, 1C, Carom), 129.3 (s, 1C, Carom), 128.9 (s, 1C, Carom), 128.2 (d, J = 11 Hz, 6C, CaromPPh3), 128 (d, J = 11 Hz, 6C, CaromPPh3), 127.7 (s, 1C, Carom), 127.3 (s, 1C, Carom), 127.2 (s, 1C, Carom), 126.7 (s, 1C, Carom), 126.3 (s, 1C, Carom), 125.5 (d, J = 10 Hz, 2C, CaromNPhF), 125.5 (d, J = 10 Hz, 2C, CaromNPhF), 124.4 (s, 1C, Carom), 124.1 (s, 1C, Carom), 117.5 (q, J = 280 Hz, 1C, CF3), 116.7 (d, J = 24 Hz, 2C, CaromNPhF), 116.7 (d, J = 24 Hz, 2C, CaromNPhF), 92.5 (q, J = 3 Hz, 1C, CH), 91.8 (q, J = 3 Hz, 1C, CH). IR (KBr): 3056 (w), 1626 (w), 1571 (s), 1484 (s), 1435 (s), 1370 (w), 1354 (w), 1298 (s), 1258 (m), 1236 (s), 1201 (m), 1135 (s), 1094 (m), 1054 (w), 1028 (w), 1008 (m), 999 (m), 961 (m), 936 (w), 910 (w), 863 (s), 841 (s), 780 (w), 749 (s), 709 (m), 692 (s), 649 (w), 617 (w), 598 (m), 578 (w), 561 (m), 544 (m), 528 (s) cm−1. ESI+ MS (m/z): 858.0913 [M − Cl]+ (calcd 858.0962), 916.0495 [M + Na]+ (calcd 916.0548), 932.0232 [M + K]+ (calcd 932.0287). [Re(NPhF)Cl2(PPh3)(tbutfac)]. [Re(NPhF)Cl3(PPh3)2] (186 mg, 0.2 mmol) was suspended in 5 mL of toluene. tert-Butyroyltrifluoroacetylmethane (Htbutfac) (0.14 mL, ∼0.8 mmol) was added, and the mixture was heated under reflux for 7 h. After the solvent had been removed under vacuum, the residue was washed with n-hexane, yielding the product as a green powder. Crystals suitable for X-ray diffraction were obtained by slow evaporation of an isopropanol/ MeOH/MeCN solution. Yield: 119 mg (70%). Elemental Anal. Calcd for C32H32NO2PCl2F4Re: C, 46.7%; H, 3.6%; N, 1.7%. Found: C, 47.5%; H, 3.7%; N, 1.6%. 1H NMR (CDCl3): δ 7.66−7.71 (m, 6H, HaromPPh3), 7.33−7.40 (m, 9H, HaromPPh3), 7.18−7.21 (m, 2H, HaromNPhF), 6.81−6.85 (m, 2H, HaromNPhF), 6,54 (s, 1H, CH), 6.41 (s, 1H, CH), 1.35 (s, 9H, CH3), 0.79 (s, 9H, CH3). 19F NMR (CDCl3): δ −72.6 (s, 3F, CF3), −73.4 (s, 3F, CF3), −103.8 (ttd, J = 7.5 Hz, J = 3.8 Hz, J = 1.1 Hz, 1F, PhF), −104.4 (ttd, J = 7.5 Hz, J = 3.8 Hz, J = 1.1 Hz, 1F, PhF). 31P NMR (CDCl3): δ −3.4 (s), −5.1 (s). 13C NMR (CDCl3): δ 207.8 (s, 1C, CO), 206.7 (s, 1C, C O), 161.5 (d, J = 240 Hz, 1C, CaromPhF), 153.4 (s, 1C, CaromPhF), 134.7 (d, J = 10 Hz, 6C, CaromPPh3), 131.4 (d, J = 56 Hz, 3C, CaromPPh3), 130 (d, J = 3 Hz, 3C, CaromPPh3), 128 (d, J = 11 Hz, 6C, CaromPPh3), 125.4 (d, J = 10 Hz, 2C, CaromPhF), 117.5 (q, J = 280 Hz, 1C, CF3), 116.7 (d, J = 24 Hz, 2C, CaromPhF), 91.8 (s, 1C, CH), 90.8 (s, 1C, CH), 28.5 (s, 1C, CH3), 27.8 (s, 1C, CH3). IR (KBr): 3059 (w), 2972 (w), 2933 (w), 1581 (s), 1531 (m), 1511 (w), 1436 (s), 1393 (w), 1365 (w), 1342 (w), 1303 (s), 1253 (m), 1228 (m), 1189 (m), 1149 (s), 1118 (m), 1096 (s), 1029 (w), 1010 (w), 1000 (w), 954 (w), 856 (w), 845 (s), 814 (w), 804 (m), 750 (s), 707 (w), 690 (s), 618 (w), 592 (m), 562 (m), 542 (m), 529 (s) cm−1. ESI+ MS (m/z): 714.0444 [M − NPhF]+ (calcd 714.0479), 788.1078 [M − Cl]+ (calcd 788.1118), 823.0793 [M]+ (calcd 823.0807), 846.0654 [M + Na]+ (calcd 846.0705), 862.0389 [M + K]+ (calcd 862.0444). X-ray Crystallography. The intensities for the crystal structure determinations of [Tc(NPh)Cl 2 (PPh 3 )(hfac)], [Tc(NPhF)Cl 2 (PPh 3 )(hfac)], [Re(NPhF)Cl 2 (PPh 3 )(hfac)], [Re(NPhF)Cl2(PPh3)(tfac)], and [Re(NPhF)Cl2(PPh3)(Buttfac)] were collected on a Bruker D8 Venture instrument at 100 K with Mo Kα radiation (λ = 0.71073 Å) using a TRIUMPH monochromator. The intensities for the crystal structure determination of [Re(NPhF)Cl2(PPh3)(acac)] were collected on a STOE IPDS II T instrument at 200 K with Mo Kα radiation (λ = 0.71073 Å) using a graphite monochromator. For data reduction and absorption correction, standard procedures were applied. Structure solution and refinement were performed with SHELXS-86, SHELXS-97, SHELXS-2014, SHELXL-97, and SHELXL-2014.30,31 Hydrogen atoms were calculated for idealized positions and treated with the “riding model” option of SHELXL.

Crystal data and structure determination parameters are given in the Supporting Information. Additional information about the structure calculations has been deposited with the Cambridge Crystallographic Data Centre.

■

RESULTS AND DISCUSSION Reactions of (NBu4)[MOCl4] (M = Tc or Re) with hexafluoroacetylacetone (Hfac) in CH2Cl2 give the ionic complexes [MOCl3(hfac)]− in good yields. Their formation is analogous to that of the rhenium acetylacetonato complex (NBu4)[ReOCl3(acac)].13 The products were isolated as their (NBu4)+ salts, forming bright yellow (Tc) or bright red (Re) solids. Complexes with more than one hfac− ligand could not be produced in this way. The IR spectra of the products show the TcO and ReO stretches at 988 and 991 cm−1, respectively. The CO bands are found in the range between 1550 and 1650 cm−1. The 1H NMR spectra show the signals of the tetrabutylammonium cation in the expected range. Each of two singlet signals is observed in the 19F NMR spectra of the products {−74.1 and −75.5 ppm for [TcOCl3(hfac)]− and −72.3 and −73.7 ppm for [ReOCl3(hfac)]−}, clearly indicating the coordination of the hfac− ligand in one plane together with the oxido ligand as is shown in Scheme 1. Scheme 1. Synthesis of (NBu4)[MOCl3(hfac)] Complexes

In contrast to the unsubstituted phenylimido complex [Re(NPh)Cl3(PPh3)2], which is insoluble in almost all common solvents, [Re(NPhF)Cl3(PPh3)2] is readily soluble in polar solvents such as CH2Cl2, CHCl3, and THF and may be used as a precursor for ongoing ligand exchange reactions. Thus, we undertook some reactions with different β-diketones. The results are summarized in Scheme 2. [Re(NPhF)Cl3(PPh3)2] reacts with acetylacetone (Hacac) as well as with hexafluoroacetylacetone (Hhfac) under replacement of the labile chlorido ligand trans to {NPhF}2− and one PPh3 ligand under formation of the rhenium(V) complexes [Re(NPhF)Cl2(PPh3)(acac)] and [Re(NPhF)Cl2(PPh3)(hfac)]. Both compounds can be isolated as green solids. The 1H NMR spectra of both compounds show wellresolved multiplets in the aromatic region, which can be assigned unambiguously. The CH groups of the acetylacetonato and hexafluoroacetylacetonato ligands give singlets at 5.94 and 6.70 ppm, respectively. The 19F NMR spectrum of [Re(NPhF)Cl2(PPh3)(acac)] gives a signal at −105.6 ppm. It is slightly shifted to higher fields in comparison to that of the starting material [Re(NPhF)Cl3(PPh3)2].19 The respective signal in the spectrum of [Re(NPhF)Cl2(PPh3)(hfac)], however, appears at 101.9 ppm and is, thus, shifted to lower field, which is probably due to the electron-withdrawing effect of the fluorine atoms of the hfac− ligand. Both signals show complex splitting patterns due to the coupling of the fluorine atom with the hydrogen atoms of the 4-fluorophenyl ring and the phosphorus atom of the PPh3 ligand, resulting each in a triplet of a triplet of a doublet. The coupling constants are D

DOI: 10.1021/acs.inorgchem.9b00326 Inorg. Chem. XXXX, XXX, XXX−XXX

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Inorganic Chemistry Scheme 2. Reactions of [Re(NPhF)Cl3(PPh3)2] with β-Diketones

slightly smaller (7.5, 3.8, and 1.1 Hz) with respect to the values found for [Re(NPhF)Cl3(PPh3)2].19 The 31P NMR spectra show relatively broad signals at −3.4 and −0.4 ppm, respectively, without resolved 19F couplings. Single crystals of [Re(NPhF)Cl2(PPh3)(acac)] and [Re(NPhF)Cl2(PPh3)(hfac)] were obtained from CH2Cl2/MeOH solutions. An ellipsoid representation of the molecular structure of [Re(NPhF)Cl2(PPh3)(hfac)] is given in Figure 1. The structure of [Re(NPhF)Cl2(PPh3)(acac)] is virtually

identical and is shown in the Supporting Information. Selected bond lengths and angles of both compounds are compared in Table 1. Table 1. Selected Bond Lengths (angstroms) and Angles (degrees) of [Re(NPhF)Cl2(PPh3)(acac)] and [Re(NPhF)Cl2(PPh3)(hfac)]

Re1−N1 N1−C11 Re1−O1 Re1−O2 Re1−P1 Re1−Cl1 Re1−Cl2 Re1−N1−C11 N1−Re1−O1 N1−Re1−Cl1 N1−Re1−Cl2 N1−Re1−P1

[Re(NPhF)Cl2(PPh3) (acac)]

[Re(NPhF)Cl2(PPh3) (hfac)]

1.707(4) 1.379(7) 2.075(4) 2.034(4) 2.450(2) 2.383(2) 2.407(2) 171.7(4) 96.8(2) 99.7(2) 94.9(2) 88.8(2)

1.715(2) 1.381(2) 2.066(2) 2.087(2) 2.428(1) 2.378(1) 2.396(1) 173.9(2) 100.67(7) 101.47(6) 93.74(6) 88.93(6)

The linearly bonded 4-fluorophenylimido ligands (the Re1− N1−C11 angles are 171.7(4)° and 173.9(2)°) and one of the oxygen donor atoms of the acetylacetonato ligands are arranged in trans positions to each other. The other oxygen donor atom, the PPh3 ligand, and the remaining two chlorido ligands form the equatorial coordination planes of the complexes. The N1−Re1−O1, N1−Re1−Cl1, and N1− Re1−Cl2 angles are all considerably larger than 90°. This socalled “roof effect” is due to the steric demand of the ReN bond and has already been described previously for phenylimidorhenium complexes.19,32 It is, however, remarkable that the N1−Re1−P1 angles are smaller than 90° in [Re(NPhF)Cl2(PPh3)(acac)] and [Re(NPhF)Cl2(PPh3)(hfac)]. No obvious bond length differences between the two complexes are observed. Thus, the fluorination of the acetylacetonato ligand

Figure 1. Molecular structure of [Re(NPhF)Cl2(PPh3)(hfac)]. Thermal ellipsoids represent 50% probability. Hydrogen atoms have been omitted for the sake of clarity. E

DOI: 10.1021/acs.inorgchem.9b00326 Inorg. Chem. XXXX, XXX, XXX−XXX

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Figure 2. 19F NMR spectrum of the structural isomers of [Re(NPhF)Cl2(PPh3)(tfac)].

Single crystals of [Re(NPhF)Cl2(PPh3)(tfac)] suitable for X-ray diffraction were obtained from a CH2Cl2/MeCN/ MeOH solution at −20 °C. The two structural isomers of [Re(NPhF)Cl2(PPh3)(tfac)] are isostructural to [Re(NPhF)Cl2(PPh3)(acac)] and [Re(NPhF)Cl2(PPh3)(hfac)] and cocrystallize in the same crystal. This results in the occupation of the same positions by the CH3 and the CF3 groups, respectively, as is shown in Figure 3. This occupational disorder has been treated during the refinement, and an approximate ratio of 3:1 in favor of the CF3 being bonded to the C2 atom has been found for the crystal used for the work

seems not to have any significant influence on the bonding situation in the complexes. [Re(NPhF)Cl2(PPh3)(acac)] and [Re(NPhF)Cl2(PPh3)(hfac)] are kinetically inert. Attemps to perform ligand exchange reactions of [Re(NPhF)Cl2(PPh3)(acac)] with hexafluoroacetylacetone and [Re(NPhF)Cl2(PPh3)(hfac)] with acetylacetone were unsuccessful. 19F NMR spectra, which were directly recorded for the reaction solutions, show only the signals of the respective starting materials. An excess of trifluoroacetylacetone (Htfac) reacts with [Re(NPhF)Cl3(PPh3)2] in boiling toluene under formation of [Re(NPhF)Cl2(PPh3)(tfac)]. Two structural isomers of the products are formed in which the CF3 group of the tfac− ligand is positioned either “cis” or “trans” to the 4-fluorophenylimido ligand. The formation of such isomers is not uncommon in the coordination chemistry of trifluoroacetylacetone. The reaction of [Ru3(CO)12] with Htfac for example leads to three isomers of [Ru(CO)2(tfac)2].33 Furthermore, structural isomers can be observed for a series of cobalt complexes with compositions of [Co(tfac)2(acac)] and [Co(tfac)3] as well as for the nickel complex [Ni(pn)(tfac)2] (pn = propylenediamine).34,35 The two isomers of [Re(NPhF)Cl2(PPh3)(tfac)] could not be separated by chromatographical methods, but they can clearly be distinguished by their NMR spectra. The singlets at 6.41 and 6.20 ppm in the 1H NMR spectrum of the obtained green solid can be assigned to the CH groups of the trifluoroacetylacetonato ligands of the two isomers. The singlets at 3.20 and 2.14 ppm belong to the respective CH3 groups. The 19F NMR spectrum shows two singlets at −72.8 and −73.6 ppm, which can be assigned to the CF3 groups of the trifluoroacetylacetonato ligands in the two isomers. Likewise, two signals for the 4-fluorophenylimido ligand at −103.8 and −103.9 ppm can be observed. These signals also show the splitting, resulting in a triplet of a triplet of a doublet (Figure 2). Integration of the respective signals gives an approximate ratio of 5:6 of the two isomers. An unambiguous assignment of the signals to individual structures, however, is not possible on the basis of the spectroscopic data.

Figure 3. Molecular structure of [Re(NPhF)Cl2(PPh3)(tfac)]. Thermal ellipsoids represent 50% probability. Hydrogen atoms have been omitted for the sake of clarity. The two CF3 groups are “disordered” in a ratio of 3:1 (A:B). F

DOI: 10.1021/acs.inorgchem.9b00326 Inorg. Chem. XXXX, XXX, XXX−XXX

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isomers with the more bulky naphtyl or tert-butyl substituents in the “equatorial” positions. Reactions of [Re(NPhF)Cl3(PPh3)2] with Hnaphtfac and Htbutfac have been performed in boiling toluene. They result in the formation of the complexes [Re(NPhF)Cl2(PPh3)(naphttfac)] and [Re(NPhF)Cl2(PPh3)(tbutfac)]. Their 19F NMR spectra (Figure 4) confirm the formation of the expected

presented here. It should, however, be mentioned that in other crystals other ratios can be found. This is also clear from the approximate 1:1 distribution of the two isomers in the reaction mixture as is seen from the NMR spectra. The bond lengths and angles in the coordination sphere of [Re(NPhF)Cl2(PPh3)(tfac)] are unexceptional and roughly in the range of those found for [Re(NPhF)Cl2(PPh3)(acac)] or [Re(NPhF)Cl2(PPh3)(hfac)] (see Table 2). Table 2. Selected Bond Lengths (angstroms) and Angles (degrees) of [Re(NPhF)Cl2(PPh3)(tfac)] and [Re(NPhF)Cl2(PPh3)(tbutfac)]

Re1−N1 Re1−O1 Re1−O2 Re1−P1 Re1−Cl1 Re1−Cl2 Re1−N1−C11 N1−Re1−Cl1 N1−Re1−Cl2 N1−Re1−P1 N1−Re1−O1

[Re(NPhF)Cl2(PPh3) (tfac)]

[Re(NPhF)Cl2(PPh3) (tbutfac)]

1.720(2) 2.068(2) 2.067(2) 2.422(1) 2.384(1) 2.404(1) 172.3(2) 101.21(6) 92.27(6) 88.48(6) 100.33(7)

1.723(3) 2.057(2) 2.071(2) 2.411(1) 2.398(1) 2.379(1) 165.7(2) 91.99(9) 104.44(8) 86.68(8) 102.6(1)

The formation of the two [Re(NPhF)Cl2(PPh3)(tfac)] isomers in an approximate ratio of 1:1 suggests that there are no significant energy differences between the two compounds and leads to the question of whether the ratio between the isomers can be controlled by the addition of more bulky substituents instead of CH3. For a first estimation, we undertook some DFT calculations for [Re(NPhF)Cl2(PPh3)(L)] complexes, where HL = Htfac, benzoyltrifluoroacetylmethane (Hphtfac), naphthoyltrifluoroacetylmethane (Hnaphtfac), or tert-butyroyltrifluoroacetylmethane (Htbutfac). For the optimization of the structures, the X-ray data of [Re(NPhF)Cl2(PPh3)(tfac)] were used as initial parameters and modified as requested. The agreement between the experimental data and the computed structural parameters for [Re(NPhF)Cl2(PPh3)(tfac)] was good. Bond lengths differ by