TY - JOUR
T1 - Twelve-Electron Organochromium Species
T2 - Synthesis and Characterization of High-Spin Square-Planar Chromium(II) Alkyls and Aryls
AU - Hermes, Ann R.
AU - Morris, Robert J.
AU - Girolami, Gregory S.
PY - 1988/11
Y1 - 1988/11
N2 - Alkylation of the chromium phosphine complex [CrCl2(dippe)]2(dippe = 1,2-bis(diisopropylphosphino)ethane) with Grignard or dialkylmagnesium reagents gives the unusual 12-electron chromium(II) alkyls cis-CrR2(dippe) (R = CH2CMe3, CH2SiMe3)C6H2Me3). The unidentate phosphine complex £ran£-Cr(C6H2Me3)2(PMe3)2 may be prepared similarly by treatment of CrCl2(THF) with dimesitylmagnesium in the presence of PMe3. All of these four-coordinate alkyls possess magnetic moments characteristic of high-spin species, μ = 4.9 μB, and exhibit broadened 1H NMR resonances consistent with the paramagnetism. X-ray crystal structures of Cr(CH2CMe3)2(dippe) and Cr(CH2SiMe3)2(dippe) reveal tetrahedrally distorted square-planar structures, where the dihedral angle between the C-Cr-C and P-Cr-P planes is larger in the neopentyl complex, 28.4° vs 15.8°, due to steric effects. For similar reasons, the Cr-C and Cr-P distances in the neopentyl compound of 2.149 (8) and 2.556 (2) ° are slightly longer than those of 2.128 (4) and 2.517 (1) ° in the (trimethylsilyl)methyl derivative, and the C-Cr-C angle is also larger in the neopentyl complex at 101.9 (3)° vs 95.7 (2)°. In contrast to these results, the mesityl complex Cr(C6H2Me3)2(PMe3)2 is essentially flat: the ipso carbon atoms and the phosphorus atoms are +0.9° and -0.9° out of the mean CrC2P2 plane, respectively. The Cr-C and Cr-P distances in this molecule are 2.130 (6) and 2.462 (2) Å, while all the C-Cr-P angles fall between 89.3 (2)° and 90.8 (2)°. Crystal data: for Cr(CH2CMe3)2(dippe), space group C2/c, a = 15.867 (5) Å, b = 10.401 (4) Å, c = 18.154 (6) Å, β = 106.67 (3)°, V = 2870 (2) Å3, Z = 4, RF = 5.9%, RwF= 7.7% on 126 variables and 1205 data; for Cr(CH2SiMe3)2(dippe), space group C2/c, a = 15.666 (4) Å, b = 10.983 (3) Å, c = 18.099 (6) Å, β = 102.43 (2)°, V = 3041 (1) Å3, Z = 4, RF = 4.1% RwF = 4.6% on 128 variables and 1472 data; for Cr(C6H2Me3)2(PMe3)2, space group P2l/n, a = 9.710 (2) Å, b = 14.121 (3) Å, c = 19.446 (3) Å, β = 98.36 (1)°, V = 2638.0 (9) Å3, Z = 4, RF = 5.1%, RwF = 6.1% on 260 variables and 2199 data. The chromium alkyls are able to polymerize ethylene slowly at 25 °C and 10 atm.
AB - Alkylation of the chromium phosphine complex [CrCl2(dippe)]2(dippe = 1,2-bis(diisopropylphosphino)ethane) with Grignard or dialkylmagnesium reagents gives the unusual 12-electron chromium(II) alkyls cis-CrR2(dippe) (R = CH2CMe3, CH2SiMe3)C6H2Me3). The unidentate phosphine complex £ran£-Cr(C6H2Me3)2(PMe3)2 may be prepared similarly by treatment of CrCl2(THF) with dimesitylmagnesium in the presence of PMe3. All of these four-coordinate alkyls possess magnetic moments characteristic of high-spin species, μ = 4.9 μB, and exhibit broadened 1H NMR resonances consistent with the paramagnetism. X-ray crystal structures of Cr(CH2CMe3)2(dippe) and Cr(CH2SiMe3)2(dippe) reveal tetrahedrally distorted square-planar structures, where the dihedral angle between the C-Cr-C and P-Cr-P planes is larger in the neopentyl complex, 28.4° vs 15.8°, due to steric effects. For similar reasons, the Cr-C and Cr-P distances in the neopentyl compound of 2.149 (8) and 2.556 (2) ° are slightly longer than those of 2.128 (4) and 2.517 (1) ° in the (trimethylsilyl)methyl derivative, and the C-Cr-C angle is also larger in the neopentyl complex at 101.9 (3)° vs 95.7 (2)°. In contrast to these results, the mesityl complex Cr(C6H2Me3)2(PMe3)2 is essentially flat: the ipso carbon atoms and the phosphorus atoms are +0.9° and -0.9° out of the mean CrC2P2 plane, respectively. The Cr-C and Cr-P distances in this molecule are 2.130 (6) and 2.462 (2) Å, while all the C-Cr-P angles fall between 89.3 (2)° and 90.8 (2)°. Crystal data: for Cr(CH2CMe3)2(dippe), space group C2/c, a = 15.867 (5) Å, b = 10.401 (4) Å, c = 18.154 (6) Å, β = 106.67 (3)°, V = 2870 (2) Å3, Z = 4, RF = 5.9%, RwF= 7.7% on 126 variables and 1205 data; for Cr(CH2SiMe3)2(dippe), space group C2/c, a = 15.666 (4) Å, b = 10.983 (3) Å, c = 18.099 (6) Å, β = 102.43 (2)°, V = 3041 (1) Å3, Z = 4, RF = 4.1% RwF = 4.6% on 128 variables and 1472 data; for Cr(C6H2Me3)2(PMe3)2, space group P2l/n, a = 9.710 (2) Å, b = 14.121 (3) Å, c = 19.446 (3) Å, β = 98.36 (1)°, V = 2638.0 (9) Å3, Z = 4, RF = 5.1%, RwF = 6.1% on 260 variables and 2199 data. The chromium alkyls are able to polymerize ethylene slowly at 25 °C and 10 atm.
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U2 - 10.1021/om00101a018
DO - 10.1021/om00101a018
M3 - Article
AN - SCOPUS:0000362925
SN - 0276-7333
VL - 7
SP - 2372
EP - 2379
JO - Organometallics
JF - Organometallics
IS - 11
ER -