An N-unprotected Fischer pyrrolidinyl­idene complex

The synthesis and crystal structure of penta­carbonyl(pyrrolidin-2-yl­idene)­chromium(0), [Cr(C₄H₇N)(CO)₅], is reported. The compound shows strong interaction between the lone pair at nitro­gen and the carbene C atom, and weak intermolecular hydrogen bonds.

S1. Comment

Fischer aminocarbene complexes are versatile reagents for stereoselective organic synthesis (Dötz, 1984; Hegedus, 1995; Wulff, 1995; Barluenga, 1996). Cycloalkylidene complexes are potential precursors for spiro-cycloaddition and annelation reactions. Oxacyclopentylidene complexes are readily accessible by cyclization of alkynols at the metal template (Dötz et al., 1987) and can be transformed into azacyclopentylidene (pyrrolidinylidene) complexes by an efficient one-pot procedure recently described by us (Haase & Dötz, 1999). The protocol is characterized by smooth conditions and provides the first generally applicable (Haase et al., 1999; Dötz et al., 1997) access to N-unprotected azacyclopentylidene complexes.

The structure was determined by X-ray crystallography to study the ring conformation and bond lengths in the absence of steric hindrance induced by substituents at the N atom. Complex (III) shows a ³E conformation, with an angle of 11.3 (3)° between the C4/N1/C1/C2 and C4/C3/C2 planes, C3 lying 0.181 (4) Å above the C4/N1/C1/C2 plane. Characteristic details are the planarity at the N and the carbene C atom which indicates the strong π-interaction between these atoms, supported by the very short nitrogen–carbene bond of 1.296 (2) Å and the minor distortions from an exact trigonal environment of the Nsp² atom [C1—N1—H1 121.7 (14)°]. In contrast, known N-methyl-substituted azacyclopentylidene complexes show major steric interactions between the pentacarbonylchromium fragment and the N-methyl group resulting in C1—N1—NCH₃ angles of 125.8 (Dötz et al., 1997) or 127.7° (Dötz et al., 1999) and longer nitrogen–carbene bonds (1.313 and 1.3059 Å, respectively). Complex (III) shows almost ideal octahedral coordination around the Cr atom. The Cr—C distance of the trans-carbonyl group is between 0.014 and 0.035 Å shorter than to the cis-carbonyl ligands, as expected for Fischer carbene complexes (Fischer, 1974). The crystal structure is stabilized by weak intermolecular hydrogen bonds [2.26 (2) Å] between the N1 H atom and the O1Eⁱ atom of a carbonyl ligand [symmetry code: (i) x + 1, y, z].

S2. Experimental

Pentacarbonyl(oxacyclopentylidene)chromium(0), (I), was subjected to ammonolysis and the intermediate formed, i.e. acyclic aminocarbene complex (II), was recyclized under Mitsunobu conditions overnight. Recrystallization of the pure product from n-pentane/dichloromethane yielded complex (III) as yellow crystals in 65% overall yield.

S3. Refinement

All H atoms were located by a difference Fourier synthesis and refined with fixed individual displacement parameters [U_iso(H) = 1.2U_eq(C or N)], using a riding model with C—H = 0.99 Å, while the coordinates of the H(N) atom were refined.

Computing details

Data collection: COLLECT (Nonius, 1998); cell refinement: DENZO-SMN (Otwinowski & Minor, 1997); data reduction: DENZO-SMN (Otwinowski & Minor, 1997); program(s) used to solve structure: SHELXS97 (Sheldrick, 1990); program(s) used to refine structure: SHELXL97 (Sheldrick, 1997); molecular graphics: SHELXTL-Plus (Sheldrick, 1991); software used to prepare material for publication: SHELXL97.

2-Azacyclopentylidene(pentacarbonyl)chromium(0)

Crystal data

[Cr(C4H7N)(CO)5]	Dx = 1.637 Mg m^−3
Mr = 261.16	Mo Kα radiation, λ = 0.71073 Å
Orthorhombic, P212121	Cell parameters from 14785 reflections
a = 6.7152 (3) Å	θ = 3.3–27.3°
b = 10.1507 (5) Å	µ = 1.08 mm^−1
c = 15.5447 (9) Å	T = 123 K
V = 1059.59 (9) Å^3	Plates, yellow
Z = 4	0.40 × 0.10 × 0.05 mm
F(000) = 528

Data collection

Nonius KappaCCD diffractometer	2402 reflections with I > 2σ(I)
Radiation source: fine-focus sealed tube	Rint = 0.035
Graphite monochromator	θmax = 28.3°, θmin = 3.3°
rotation in ϕ and ω, 2° scans	h = −8→8
14711 measured reflections	k = −13→13
2630 independent reflections	l = −20→20

Refinement

Refinement on F^2	Secondary atom site location: difference Fourier map
Least-squares matrix: full	Hydrogen site location: inferred from neighbouring sites
R[F^2 > 2σ(F^2)] = 0.024	H atoms treated by a mixture of independent and constrained refinement
wR(F^2) = 0.057	w = 1/[σ^2(Fo^2) + (0.0307P)^2] where P = (Fo^2 + 2Fc^2)/3
S = 1.02	(Δ/σ)max = 0.001
2630 reflections	Δρmax = 0.25 e Å^−3
148 parameters	Δρmin = −0.22 e Å^−3
1 restraint	Absolute structure: Flack (1983); 1097 Friedel pairs
Primary atom site location: Patterson	Absolute structure parameter: −0.015 (17)

Special details

Experimental. Absorption correction using SHELXTL-Plus and MULABS (Blessings algorithm) don't improve the data.

dx = 39.880 (4) mm; 2 x 90 sec., 2 °., 279 frames; mos.= 0.744 (3)

Geometry. All e.s.d.'s (except the e.s.d. in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell e.s.d.'s are taken into account individually in the estimation of e.s.d.'s in distances, angles and torsion angles; correlations between e.s.d.'s in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell e.s.d.'s is used for estimating e.s.d.'s involving l.s. planes.

Refinement. Refinement of F² against ALL reflections. The weighted R-factor wR and goodness of fit S are based on F², conventional R-factors R are based on F, with F set to zero for negative F². The threshold expression of F² > σ(F²) is used only for calculating R-factors(gt) etc. and is not relevant to the choice of reflections for refinement. R-factors based on F² are statistically about twice as large as those based on F, and R- factors based on ALL data will be even larger.

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Ų)

	x	y	z	Uiso*/Ueq
Cr1	0.32622 (4)	0.31481 (3)	0.307789 (17)	0.01860 (8)
C1A	0.2411 (3)	0.19876 (18)	0.22144 (11)	0.0241 (4)
O1A	0.1875 (2)	0.12955 (14)	0.16777 (8)	0.0330 (3)
C1B	0.2120 (3)	0.45717 (19)	0.24477 (11)	0.0238 (4)
O1B	0.14254 (19)	0.54057 (14)	0.20615 (8)	0.0342 (3)
C1C	0.4376 (3)	0.17510 (19)	0.37240 (11)	0.0231 (4)
O1C	0.5022 (2)	0.08924 (14)	0.41127 (9)	0.0336 (3)
C1D	0.5750 (3)	0.34191 (18)	0.25094 (11)	0.0235 (4)
O1D	0.7233 (2)	0.35719 (14)	0.21661 (9)	0.0346 (3)
C1E	0.0839 (3)	0.29405 (17)	0.36800 (11)	0.0214 (4)
O1E	−0.06250 (19)	0.28133 (13)	0.40525 (9)	0.0278 (3)
N1	0.5664 (2)	0.44329 (16)	0.45095 (10)	0.0258 (3)
H1	0.652 (3)	0.3807 (17)	0.4462 (13)	0.031*
C1	0.4092 (3)	0.44857 (17)	0.40267 (11)	0.0193 (3)
C2	0.2968 (3)	0.56986 (18)	0.43046 (13)	0.0293 (4)
H2A	0.1692	0.5447	0.4578	0.035*
H2B	0.2677	0.6264	0.3801	0.035*
C3	0.4276 (3)	0.6433 (2)	0.49435 (15)	0.0434 (6)
H3A	0.3514	0.6664	0.5467	0.052*
H3B	0.4809	0.7251	0.4685	0.052*
C4	0.5952 (3)	0.54790 (19)	0.51559 (12)	0.0270 (4)
H4A	0.7272	0.5904	0.5092	0.032*
H4B	0.5820	0.5129	0.5748	0.032*

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
Cr1	0.01866 (12)	0.01926 (13)	0.01787 (12)	0.00060 (11)	0.00123 (11)	−0.00015 (11)
C1A	0.0250 (8)	0.0250 (9)	0.0222 (8)	0.0026 (8)	0.0038 (7)	0.0040 (8)
O1A	0.0415 (8)	0.0335 (7)	0.0241 (6)	−0.0022 (7)	−0.0013 (6)	−0.0086 (6)
C1B	0.0217 (10)	0.0284 (9)	0.0214 (8)	−0.0007 (8)	0.0031 (7)	−0.0022 (8)
O1B	0.0342 (8)	0.0358 (7)	0.0326 (8)	0.0070 (6)	−0.0015 (6)	0.0116 (6)
C1C	0.0219 (8)	0.0250 (9)	0.0223 (8)	−0.0026 (8)	0.0047 (7)	−0.0036 (8)
O1C	0.0377 (8)	0.0296 (7)	0.0333 (8)	0.0066 (6)	0.0025 (6)	0.0083 (6)
C1D	0.0291 (10)	0.0228 (10)	0.0185 (8)	0.0006 (8)	−0.0011 (8)	−0.0007 (7)
O1D	0.0289 (7)	0.0413 (8)	0.0338 (8)	−0.0016 (6)	0.0102 (6)	0.0036 (6)
C1E	0.0254 (8)	0.0183 (9)	0.0206 (8)	0.0015 (7)	−0.0039 (7)	−0.0008 (7)
O1E	0.0220 (6)	0.0305 (7)	0.0310 (7)	0.0004 (5)	0.0058 (5)	−0.0025 (6)
N1	0.0229 (8)	0.0263 (8)	0.0281 (8)	0.0064 (7)	−0.0019 (7)	−0.0058 (7)
C1	0.0202 (8)	0.0201 (9)	0.0175 (8)	−0.0018 (7)	0.0022 (7)	0.0037 (7)
C2	0.0279 (11)	0.0266 (10)	0.0333 (10)	0.0050 (8)	−0.0038 (8)	−0.0032 (8)
C3	0.0421 (13)	0.0421 (13)	0.0461 (14)	0.0149 (10)	−0.0152 (10)	−0.0200 (11)
C4	0.0280 (9)	0.0280 (10)	0.0249 (9)	0.0003 (8)	−0.0043 (8)	−0.0047 (8)

Geometric parameters (Å, º)

Cr1—C1A	1.8751 (19)	N1—C4	1.475 (2)
Cr1—C1E	1.8892 (18)	N1—H1	0.862 (15)
Cr1—C1C	1.892 (2)	C1—C2	1.507 (3)
Cr1—C1B	1.9069 (19)	C2—C3	1.521 (3)
Cr1—C1D	1.9097 (19)	C2—H2A	0.9900
Cr1—C1	2.0808 (18)	C2—H2B	0.9900
C1A—O1A	1.148 (2)	C3—C4	1.521 (3)
C1B—O1B	1.138 (2)	C3—H3A	0.9900
C1C—O1C	1.146 (2)	C3—H3B	0.9900
C1D—O1D	1.140 (2)	C4—H4A	0.9900
C1E—O1E	1.148 (2)	C4—H4B	0.9900
N1—C1	1.296 (2)
C1A—Cr1—C1E	91.26 (7)	C4—N1—H1	120.1 (14)
C1A—Cr1—C1C	91.70 (8)	N1—C1—C2	105.99 (15)
C1E—Cr1—C1C	89.66 (7)	N1—C1—Cr1	126.99 (13)
C1A—Cr1—C1B	89.18 (8)	C2—C1—Cr1	127.01 (12)
C1E—Cr1—C1B	89.57 (7)	C1—C2—C3	107.37 (15)
C1C—Cr1—C1B	178.84 (8)	C1—C2—H2A	110.2
C1A—Cr1—C1D	91.49 (8)	C3—C2—H2A	110.2
C1E—Cr1—C1D	177.25 (8)	C1—C2—H2B	110.2
C1C—Cr1—C1D	90.44 (8)	C3—C2—H2B	110.2
C1B—Cr1—C1D	90.29 (8)	H2A—C2—H2B	108.5
C1A—Cr1—C1	177.43 (8)	C2—C3—C4	104.89 (16)
C1E—Cr1—C1	87.27 (7)	C2—C3—H3A	110.8
C1C—Cr1—C1	90.39 (7)	C4—C3—H3A	110.8
C1B—Cr1—C1	88.71 (7)	C2—C3—H3B	110.8
C1D—Cr1—C1	89.98 (7)	C4—C3—H3B	110.8
O1A—C1A—Cr1	178.78 (16)	H3A—C3—H3B	108.8
O1B—C1B—Cr1	178.80 (17)	N1—C4—C3	102.31 (15)
O1C—C1C—Cr1	178.81 (16)	N1—C4—H4A	111.3
O1D—C1D—Cr1	179.44 (18)	C3—C4—H4A	111.3
O1E—C1E—Cr1	179.41 (15)	N1—C4—H4B	111.3
C1—N1—C4	118.15 (15)	C3—C4—H4B	111.3
C1—N1—H1	121.7 (14)	H4A—C4—H4B	109.2
C1E—Cr1—C1A—O1A	90 (8)	C1D—Cr1—C1E—O1E	−48 (16)
C1B—Cr1—C1A—O1A	0 (8)	C1—Cr1—C1E—O1E	−47 (15)
C1D—Cr1—C1A—O1A	−90 (8)	C4—N1—C1—C2	−0.1 (2)
C1—Cr1—C1A—O1A	35 (9)	C4—N1—C1—Cr1	−179.01 (13)
C1A—Cr1—C1B—O1B	4 (8)	C1E—Cr1—C1—N1	123.34 (17)
C1E—Cr1—C1B—O1B	−87 (8)	C1C—Cr1—C1—N1	33.70 (17)
C1C—Cr1—C1B—O1B	−136 (7)	C1B—Cr1—C1—N1	−147.03 (17)
C1D—Cr1—C1B—O1B	96 (8)	C1D—Cr1—C1—N1	−56.75 (17)
C1A—Cr1—C1C—O1C	−45 (8)	C1A—Cr1—C1—C2	−0.2 (17)
C1E—Cr1—C1C—O1C	46 (8)	C1E—Cr1—C1—C2	−55.34 (16)
C1B—Cr1—C1C—O1C	95 (9)	C1C—Cr1—C1—C2	−144.98 (16)
C1D—Cr1—C1C—O1C	−136 (8)	C1B—Cr1—C1—C2	34.29 (16)
C1—Cr1—C1C—O1C	134 (8)	C1D—Cr1—C1—C2	124.58 (16)
C1A—Cr1—C1D—O1D	−18 (20)	N1—C1—C2—C3	7.2 (2)
C1C—Cr1—C1D—O1D	74 (20)	Cr1—C1—C2—C3	−173.85 (14)
C1B—Cr1—C1D—O1D	−107 (20)	C1—C2—C3—C4	−11.1 (2)
C1A—Cr1—C1E—O1E	135 (15)	C1—N1—C4—C3	−6.9 (2)
C1C—Cr1—C1E—O1E	44 (15)	C2—C3—C4—N1	10.4 (2)
C1B—Cr1—C1E—O1E	−135 (15)