A simple graphical method for analysis of lanthanide induced shifts

TetrahedronLetters No. 41, pp 4155 - 4156, 1972.

Printed in Great Britain.

PerSamenPress.

A SIMPLE GRAPHICAL METHOD FOR ANALYSIS

udwrizwmEINDUCED SHIFTS

OF

Richard M. Wing,* Thomas A. Early University

of California,

Riverside,

California

92502

and J. John Uebel* University

of New Hampshire,

Durham, New Hampshire

03824

(Receivedin USA 25 July 1972; received in UK for public&ion 5 Ssptsmkr 1972) The McConnell,

Robertson

equation'

(1) has been extensively

used in quanti-

(1)

&Ii/H = k(3 co~'e~-l)*R~-~ tative interpretations

of lanthanide

tice, for reasons of simplicity dependencies however,

and analyze

formational

is common practo ignore angular It is clear,

the LIS using the radial term only.2,3

in a number of cases.5

The use of LIS for structural

analysis, of course, requires averaging

site and rotamer populations

extant

tecnniques,

the computational

like to present

requirements

the contributions

in solution.5

ysis of tne problem can be readily accomplished would

It

(LIS).

that omission of the angular term leads to poor fits4 as well as incor-

rect assignments various

induced shifts

and rapidity of computation,

Although

and conof all the

a full anal-

by any of several optimization

are generally

a graphical method whose merit

Therefore, we

large.

is extreme simplicity with

little sacrifice of accuracy. At the heart of this method symmetric

lathanide complex

Dreiding models,

the molecule

the principal magnetic the metal. to match

axis

The relative

the observed

is best illustrated using pyridine

as examples.

ward, since symmetry requirements fore positions

(1)) drawn to the same scale as standard

The method

figure 1.

cis-4-t-butylcyclohexanol

is a map of the dipolar field for an axially

(equation

The analysis of pyridine

place the metal on its C2 axis.

molecular

(X) and the nitrogen

lies about 3.0

shifts are then read directly

shifts

the rotamer averaged mirror plane.

Cme there-

on the graph such that the ~2 axis coincidoes with l

0.5 A away from

from the plot and scaled

(Table I).

The analysis of cis-4-t-butylcyclohexanol molecule

and

is straightfor-

is a bit more complex.

For this

field must have a mirror plane coincident with the

Once again we position

the coordination

site

(OH) about

3.0 $: 0.5 w from the metal with a metal-oxygen-carbon bond angle of about 125 We also require tnat the metal oxygen bond coincide with the Principal

15O.

magnetic

axis.

One next estimates

the proton coordinates

4153

Xi and ri, where Xi

l

Ho. 41

4154

‘I

\

.-2,. .-

-_

,,/

-, ‘.

-\

Figure

1:

Map x2

of

the

example authors.

Dipolar pyridine

+ r2. 1.

~~11

Field: has size

(3cos28-l)-RW3

been copies

placed of

on

this

where the map

map

are

X = RcoSe

and

as discussed available

from

R2 =

in the

268 257

B3 81 a2

H4 trans 66 70

H4 cis 87 93

H3e 6.7 6.7

H2a 8.2 9.0

H3 28.0 29.4

*3a 13.6 14.4 *4a 6.5 6.5 2.8 2.9

t-Bu

d $ =

7s

7.6(at 2.3 g, 180')

6.0(at 3 P, 110')

1167 (1970).

g (shift observed - shift calculated)2/(shift observed)2; g(s) = 100 g

=G. I-l. Wahl and M. R. Peterson, Jr.,

g(Rd l.B(at 3 i, 180')

. 817 (1971). aC. .Beaute,2. W. Walkowski, and N. Thoai, Tetrahedron w., b P. V. Bemarco, T. R. Elzey, R. B. Lewis and E. Wenkert, 2. Amer. e. E., s, 5736 (1970).

observed calculated

l-Adamantanol:' B2

lI2e 14.9 14.4

cis-4-&-Butylcyclohexanol: b 'le observed 24.1 calculated 23.1

observed calculated

B2 35.1 34.9

Bl 90.0 08.8

pyridine:a

Table I

No. 41

4156

is the projected

distance along the principal magnetic

Figure 2:

Coordinate

axis

(x) and ri is the

system for using the dipolar

field

map with non-planar molecules. are then plotted on the dipolar field map to obtain the relative shifts. ment of the coordination optimize

distance and the metal-oxygen-carbon

the fit is straightforward.

clohexanol

and l-adamantanol

Adjust-

bond angle to

The results for pyridine,

cis-4-t-butylcy-

are given in Table I.

We feel this graphical method

represents a useful laboratory aid and for

many applications may be a satisfactory

substitute

for computer optimized

fits.4,6

References 1.

H. M. McConnel

2.

R. Caple and S. C. Kuo, Tetrahedron

and R. E. Robertson, 2. Chem. Phys., 3, Lett., 4413

1361 (1958).

(1971) and references

therein. 3.

For a recent survey see WQeW.

4.

Amer. Chem. E., 93, 6800 (1971). -M. R. Willcott, R. E. Leninski and R. E. Davis,

5.

J. J. Uebel and R. M. Wing, submitted.

6.

Horrocks,

Jr., and J. P. Snipe, III, 2. ibid., ‘$I,

(a) J. Briggs, F. A. Hart, and G. P. MOSS, -them. comm., ibid., 1285 (1971).

S. Farid, A. Atoza, and M. Maggio,

1742 (1972).

1506 (1970).

(b)

,