Inorganic Chemistry, Vol. 15, No. 6, 1976 1381
Bis(~5-isodicyclopentadienyl)nickel(11)
Contribution from the Department of Chemistry, University of California, Riverside, California 92502
Angular Dependence of Hydrogen Magnetic Resonance Contact Shifts in Substituted Nickelocenes. Molecular Structure of Bis( ~5-isodicyclopentadienyl)nickel(II) WILLIAM T. SCROGGINS, MICHAEL F. RETTIG,* and RICHARD M. WING AIC5089 1D Received September 22, 1975 Distributions of unpaired electron spin density in a series of ring-substituted nickelocenes, specifically designed to test spin delocalization mechanisms, have been measured by proton nuclear magnetic resonance methods. Contact shifts of the cyclopentadienyl ring hydrogens are quite constant (250 f 19 ppm) over the series of seven variously substituted nickelocenes, while in contrast the (0)hydrogen atoms on ( a ) carbons directly attached to the cyclopentadienyl rings exhibit contact shifts which range from zero to -312 ppm. These 0 contact shifts are shown to vary as (cos2 cp), where cp is the dihedral angle between the cyclopentadienyl pz orbital and the C,-Ho bond. In two nickelocenes with rigid substituents, large contact shifts for hydrogens remote from the cyclopentadienyl ring are observed when the “W arrangement” of the remote C-H bond and a cyclopentadienyl pz orbital is satisfied. For one such hydrogen atom a remote shift of -95.6 ppm is observed, while its geminal counterpart experiences no significant contact shift. The structure of one of the nickelocenes, bis(~5-isodicyclopentadienyl)nickel(II), was determined by an x-ray diffraction study. The compound was found to be the C2 symmetry isomer with the methylene bridges directed toward the nickel. The cyclopentadienyl rings are eclipsed and the nickel-ring perpendicular distance 1.824 (3) A agrees very well with electron diffraction result for nickelocene (1 3 2 8 A). Two formula units of the metallocene were distributed on the twofold symmetry sites (4e) of a monoclinic cell (C2/c) of dimensions a = 18.898 (4) A, b = 7.578 (3) A, c = 10.967 (4) A, and 0 = 109.5 (1)’. The disagreement factor for 1621 diffractometer-collected reflections was 0.056, based on F.
Introduction Nuclear magnetic resonance spectra which show Fermi contact interactions have been extensively used to obtain information about the bonding and electronic configuration of paramagnetic molecules.2 The bis(v-cyclopentadieny1)metal(I1) compounds (metallocenes) of the first transition series have yielded a great deal of contact shift data of theoretical i n t e r e ~ t .Several ~ interpretations of these data have been put forward. Levy and Orge14 attempted to explain the metallocene contact shift data by proposing either spin polarization (M = V; Cr) or electron delocalization (M = c o , Ni) from metal to ligand a orbitals. Fritz, Keller, and Schwarzhans5 proposed the additional possibility of direct metal-hydrogen orbital overlap. Rettig and D r a g 0 ~ ~and 5~ Prins7 also included the possibility of electron delocalization through the u (in-plane) orbitals. In the present work cyclopentadienes 1-5 were utilized in
la, R = H b,R=D
2a, R = H b,R=D
4
3
5
the preparation of substituted nickelocenes 6-10. We report
N1/2
Nil2
6a, R = H
NI / 2
7a
7b
b,R=D n
here the synthesis, characterization, and hydrogen magnetic resonance spectra of nickelocenes 6-10, and we show that the observed contact shifts are in agreement with the n-electron delocalization modeL4-’ This work provides the first extensive investigation of substituted nickelocenes. A number of such compounds have been reported previously,8 but, with the exception of 1,l ‘-dimethylnickelocene, neither N M R nor crystallographic studies have been performed. The x-ray-determined crystalline structure reported here of bis(~5-tricyclo[5.2.1.02~6]deca-2,4-dien-6-yl)nickel(II), 6a (common name bis(~5-isodicyclopentadienyl)nickel(II)) is the first completed structure in the solid state of a bis(cyc1opentadienyl)nickel(II) compound and is the only reported structure of any kind of a substituted nickelocene. Results 1. Synthesis. Organic compounds prepared for this study were synthesized as outlined in eq 1-4. Nickelocenes 6-10 were prepared in good yields by reaction of NiBrz(g1yme) with the lithium salts of the anions of 1-5, respectively. 2. Crystalline Structure of Bis(~-,~-tricycl0[5.2.1.0~~~]deca-2,4-dien-6-yl)nickel(II), 6a. The nickel atom was found to lie on a crystallographic twofold axis and thus the atom positions of the second ligand are dependent on the first. Only one set of ligand atom positional and thermal parameters were refined and the values for the other ligand atoms were generated by a twofold rotation. Final atom coordinates and bond distances are presented in Tables I and 11, respectively, and two views of the molecule are shown in Figures 1 and 2. The cyclopentadienyl ring carbons are coplanar within 0.2’. The ring hydrogens are not significantly out of the cyclopentadienyl plane within the precision of the results (standard deviation a = 5.6’): H3 is 8.5’ out of plane away from the nickel, H4 is 2.2’ out of plane away from the nickel, and H5 is 0.2’ out of plane toward the nickel. C1 and C7 are bent out of the plane of the cyclopentadienyl ring by 6.9’ away from the nickel (a = 0.14’). The two cyclopentadienyl rings are coplanar within 0.2’, with a mean ring-ring perpendicular distance of 3.648 (12) A. Closest crystallographic nickelhydro en contacts are with H1 (3.84 A), H3 (2.97 A), H4 H5 (2.86 A), H7 (3.78 A), and HlOS (3.12 A). The (2.86 dihedral angle made by the C1-H bond with the cyclopentadienyl ring (the angle between the C2-Cl-Hl plane and the C2-C3-C4-C5-C6 plane) is 19 & 3 O .
i),
I
I
I
N1/2
a
NI /2
N1/2
9
10
1382 Inorganic Chemistry, Vol. 15, No. 6, 1976
Scroggins, Rettig, and Wing
Table I. Positional and Thermal Factors for Bis(qs-tricyclo[5 .2.1 .02~6]deca-2,4-dien-6-yl)nickel(II), 6a Atom Ni
c1
c2 c3 c4 c5 C6 c7 C8 c9 C10
xa
Y
Z
0.0 0.1546 (2) 0.1194 (2) 0.1119 (2) 0.0807 (2) 0.1119 (2) 0.0940 (2) 0.1121 (2) 0.1990 (2) 0.2278 (2) 0.1042 (2)
0.1368 (1) 0.3171 (5) 0.1922 (4) 0.0118 (4) 0.0061 (5) 0.0118 (4) 0.2965 (4) 0.4856 (5) 0.5016 (6) 0.3863 (6) 0.4802 (5)
0.25 10.2142 (4) 0.2848 (3) 0.3119 (4) 0.4136 (4) 0.3119 (4) 0.3693 (3) 0.3488 (4) 0.4089 (5) 0.3168 (5) 0.2041 (4)
Atom
X
Y
H1 H3 H4 H5 H7 H8N
0.162 (5) 0.132 (5) 0.068 (6) 0.048 (5) 0.090 (5) 0.221 (5)
0.267 (13) -0.092 (13) -0.091 (14) 0.219 (13) 0.571 (13) 0.462 (13)
2
0.131 (8) 0.0278 (10) 0.465 (10) 0.520 (9) 0.386 (9) 0.493 (9)
Bllb
B22
15 (1) 72 (2) 24 (1) 128 (8) 17 (11) 85 (6) 18 (1) 89 (7) 22 (1) 125 (8) 22 (1) 174 (9) 1 8 (1) 93 (7) 25 (1) 85 (7) 27 (2) 127 (9) 20 (1) 159 (9) 25 (2) 117 (8) B. Az Atom
1.4 (1.0) 2.0 (1.1) 3.1 (1.3) 1.7 (1.0) 0.9 (0.9) 0.6 (0.9)
H8X H9N H9X HlOA HlOS
5 3 3
45 (1) 71 (4) 58 (4) 99 (5) 71 (4) 42 (4) 50 (4) 88 (5) 90 (5) 99 (5) 86 (5)
B,,
OC
9 (3) 22 (2) 12 (2) 14 (2) 7 (2) 8 (2) 11 (2) 20 (2) 9 (2) 19 (2) 12 (2)
-7 (3) 10) 6 (2) -5 (3) -18 (3) -6 (2) -7 (3) -25 (3) -13 (3) -3 (3) V
X
0.217 0.264 0.259 0.128 0.052
51,
(6) (5) (5) (5) (5)
0.611 (14) 0.297 (13) 0.469 (12) 0.595 (13) 0.472 (12)
Z
0.414 0.366 0.279 0.175 0.247
(11) (9) (9) (9) (9)
52,
OC 10 (5) 3 (4) 18 (5) 42 (5) 8 (4) -2 (4) -7 (5) -4 (5) 26 (6) 39 (5) B. A' 3.6 (1.5) 1.1 (0.9) 1.3 (1.0) 2.0 (1.1) 0.3 (0.8)
Standard deviations of last significant figures are given in parentheses. Temperature factors (Bij) for Ni and C are multiplied by l o 4 ; T = exp[-(h2B,, + k2B,, + PB,, + 2hkB,, + 2hlB,, + 2klB,,)]. B,, and B,, are required as a result of the C, site symmetry to be zero. Table 11. Bond Distances (A) in ]deca-2,4-dien-6-yl)nickel(II), 6au Bis(q5-tricyclo [ 5.2.1 .02*6
&*&J
Nix2 2.200 (3) C7-C8 1.556 (6) Ni-C3 2.208 (3) C7-C10 1.544 (7) Ni-C4 2.167 (4) C8-C9 1.563 (8) 2.183 (4) C1-H1 1.04 (10) Nix5 2.186 (3) C3-H3 Ni-C6 1.00 (11) Cl-C2 1.510 (6) C4-H4 1.00 (12) Cl-C9 1.553 (5) C5-H5 1.01 (11) 1.542 (6) C7-H7 C1-C10 0.95 (11) C2-C3 1.417 (5) C8-H8N 0.94 (9) C2C6 1.418 (5) C8-H8X 0.88 (11) C3C4 1.426 (7) C9-H9N 1.06 (9) c4c5 1.424 (5) C10-H1OA 1.08 (10) 1.508 (5) C10-H1OS 0.99 (8) C6-C7 Standard deviations are given in parentheses; x-ray crystallographic C-H bond distances are too short by -0.13
1
12a, R = H b,R=D
11
13a, 8X, 9X = H b,8X,9X=D
Table 111. Observed and Calculated NMR Shifts for Tricyclo [5.2.1 .02 .6]deca4-en-3-ol, 13a, + Eu(dpm), Shift 6 , Hz Hydrogen Shift 6 , Hz Hydrogen no. Obsd Calcdbqc no. Obsd Calcdbsc 1 304 291 8N 233 254 2 840 831 8X 176' 172 3 1304 1308 9N 272 294 4 848 825 9X 168a 140 5 610 609 10.4 184 192 6 497 508 10s 242 250 7 282 286 a Not observed in 13b. See ref 10 for computational details. Goodness of fit R I 2= c(obsd - calcd)2/cobsd2. R , = 0.036 with Eu-0 = 2.44 f 0.10 A and Eu-OC = 130 ? 20".
14
15a, R = H b,R=D
Na(CgHg)
+ RBr
NaBr t
*R
4, R = CH(CH,), 5 , R = CH(CH,CH,),
3. Characterization of 8,9-exo,exo-Dideuteriotricyclo[5.2.1.02,6]deca-4-en-3-ol,13b. Reduction of dicyclopentadiene with D2 using Pd on C catalyst, followed by oxidation with SeO2, yielded 13b, 98% dideuterated (see Experimental Section). Comparison of the NMR spectra of the dideuterated 13b and undeuterated 13a showed that the highest field signal, a broad singlet at 6 0.88, had decreased by an integral of two hydrogens. In an attempt to assign the NMR spectrum of 13a, both the dideuterated and undeuterated compounds were titrated with tris(dipivaloylmethanato)europium(III), Eu(dP43.
In 13a, the hydrogens in the cyclopentenol ring showed large downfield shifts, linear with the addition of Eu(dpm)3. The hydrogens in the norbornane ring showed much smaller shifts upon the addition of Eu(dpm)3. In addition, large geminal couplings of 8N-8X, 9N-9X, and 10A-10s and large vicinal couplings of 8N-9N and 8X-9X obscured the individual resonances. The spectra obtained by Eu(dpm)3 addition to 8X,9X-dideuterated 13b simplified the high-field region greatly. With the removal of the 8X and 9X resonances and the absence of the 8N-8X and 9N-9X couplings the linear shifts of the remaining hydrogens could be followed readily. Undeuterated 13a showed two peaks consistently to higher field that were absent in dideuterated 13b. The observed shifts for the last addition of Eu(dpm)3 to 13a were used to assign the spectra. The observed and calculated shifts for the final
Inorganic Chemistry, Vol. 15, No. 6,1976 1383 Table IV. Proton-Proton Coupling Constants, J x y , for 8,9-exo,exo-Dideuteriotricyclo [ 5.2.1.02 8~ Ideca-4-en-3-01, 13b Protons Obsd J x y Expected X Y cl, Hz J x v , Hz
n
1 2 5 4.3-4.8a 2 3
