Reactions of Coordinated Ligands and Homogeneous Catalysis

8 The Reactions of Coordinated Ligands V. Metal Complexes of β-Mercaptoamines and Their Reactions with Alkyl Halides DARYLE H. BUSCH, JOHN A. BURKE, Jr., DONALD C. JICHA, MAJOR C. THOMPSON, and MELVIN L. MORRIS Evans and McPherson Chemical Laboratories, State University, Columbus, Ohio

The

Ohio

Downloaded by MIT on July 20, 2013 | http://pubs.acs.org Publication Date: January 1, 1962 | doi: 10.1021/ba-1963-0037.ch008

The ligands NH CH CH SH, CH N(CH CH SH) , and 2

2

2

3

2

2

2

HSCH CH N=C(CH )C(CH )=NCH CH SH have been 2

2

studied.

3

2

2

trimeric n+

2

2

2

2

The first forms monomeric complexes,

[Ni(NH CH CH S) ] S) } ]

3

2

and

2

complex and

[Co(NH CH CH S) ], 2

cations,

2

2

2

[M{M"(NH CH CH S) } ] . 2

2

3

2

2

The sec

n+

2

and

3

[M{M'(NH CH CH 2

ond ligand readily forms neutral dimeric com plexes

of

the

form

[M {CH N(CH CH S) } ]. 2

3

2

2

2

2

The tetradentate ligand forms monomeric square planar complexes.

Synthetic and kinetic studies

reveal that the coordinated mercapto group may be converted into the coordinated thioether func tion without breaking the metal-sulfur bond. The nucleophilic power of the coordinated mercapto group exceeds that of RSH, but depends on the metal atom.

Bridging protects the sulfur atom

from alkylation.

In the case of nickel(II), alkyla-

tion is accompanied by expansion of the coordina tion number of the nickel from 4 to 6.

Ligand re

actions have led to the synthesis of planar ligands completely cyclized about the metal ion.

investigations

d e d i c a t e d to t h e s t u d y o f t h e r e a c t i o n s o f c o o r d i n a t e d l i g a n d s

are m o s t l i m i t e d b y the n o n a v a i l a b i l i t y of a p p r o p r i a t e complexes,

particularly the coordinated mercaptide

of s i m p l e m e r c a p t a n s a n d of c h e l a t i n g usually of v e r y

n u m b e r of years ago, E w e n s coordinated

mercaptide

and Gibson

function by

(8)

carrying

captoethylaminegold(III) with alkyl halides Et Au(NH GH CH S) + 2

2

2

2

R X

group.

dimercaptides

l o w solubility and, i n general,

well characterized T h e metal

like the

exhibit

polymeric

demonstrated out

the

the

reaction

( E q u a t i o n 1).

2

2

2

derivatives sulfides

structures.

reactivity of

of

are A the

diethyl-£-mer-

I n v i e w of the ability

[Et Au(NH CH GH S 2

metal

often metal

R)]X

125 In Reactions of Coordinated Ligands; Busch, D.; Advances in Chemistry; American Chemical Society: Washington, DC, 1962.

(1)

ADVANCES IN CHEMISTRY SERIES

126

of c o o r d i n a t e d m e t a l ions to i n f l u e n c e the c o u r s e of m a n y c o m p l e x reactions, ticularly those w h i c h

occur

par

i n living organisms, a general investigation into

the

reactivity of the c o o r d i n a t e d s u l f u r a t o m i n the p r e s e n c e of s i m p l e a l k y l a t i n g agents might

be

expected

to

yield

significant results.

However,

the

u n a v a i l a b i l i t y of

suitable complexes has r e n d e r e d s u c h studies i m p o s s i b l e i n the past. of investigations s u m m a r i z e d here, and

trimeric

complexes

I n the

course

a substantial n u m b e r of m o n o m e r i c , d i m e r i c ,

of β - m e r c a p t o e t h y l a m i n e

and

N-methyl-bis-/3-mercapto-

ethylamine a n d similar ligands have been prepared in pure f o r m a n d character ized.

These

substances

have

then

been

subjected

to

the

action

of

common

alkylating agents a n d the reactions h a v e b e e n studied i n v a r y i n g detail.

T h e re

action products have b e e n characterized b y synthetic means a n d , i n two the results of d e t a i l e d k i n e t i c m e a s u r e m e n t s

have yielded

instances,

additional information


o n t h e n a t u r e o f t h i s class o f r e a c t i o n .

Complexes of β-Mercaptoamines

and Related

Ligands

Neutral Complexes of Formulas M ( N H C H C H S ) and M ( N H C H C H S ) . 2

2

2

W e l l d e f i n e d m o n o m e r i c c o m p l e x e s of n i c k e l ( I I ) ,

2

2

palladium (II),

h a v e b e e n o b s e r v e d to f o r m w i t h ^ - m e r c a p t o e t h y l a m i n e . captoethylamine)-nickel(II), he was

NiL ,

was

2

first

to

Busch be

d e t e r m i n e d the magnetic

(16)

diamagnetic,

nickel(II)

which

is

CoL ,

These in

salt.

polar

however, Jicha

square

planar

configuration

it for

prepared yellow b i s ( β - m e r c a p t o -

blue

tris

(^-mercaptoethylamine)-co (6,

9,

10,

and

21)

(17).

compounds both

strongly basic

a

(16)

Light

2

bis(/3-mer-

(15);

of this substance.

has b e e n p r e p a r e d b y several investigators

3

s h o w n to b e d i a m a g n e t i c

soluble

PdL .

3

(III)

m o m e n t of this c o m p l e x a n d f o u n d

with

T h e same investigators

(16).

ethylamine)-palladium (II), balt (III),

consistent

2

survey of f o u r - c o o r d i n a t e n i c k e l (II)

complexes a n d d i d not make a detailed characterization and

T h e green

prepared b y Jensen

primarily concerned w i t h a general

2

a n d cobalt

share and

the

common

nonpolar

property

solvents

and

solutions c o n t a i n i n g stoichiometric

of

are

being

only

readily

amounts

of

sparingly

deposited

ligand

and

A l t h o u g h the a p p l i c a t i o n of this s i m p l e p r o c e d u r e results i n the

of p u r e crystalline solids i n the

case of the

n i c k e l (II)

from metal

formation

a n d p a l l a d i u m (II)

com

plexes, the isolation of the cobalt c o m p l e x , C o L , b y the e x t e n d e d air oxidation of 3

the c o b a l t (II)

c o m p l e x i n a q u e o u s s o l u t i o n is d i f f i c u l t b e c a u s e

nature of the solid.

of the

gelatinous

M e t h o d s b a s e d o n the d i s p l a c e m e n t of other l i g a n d s f r o m the

c o o r d i n a t i o n sphere of cobalt (III)

by N H

2

C H

2

C H

2

S

have been more

_

successful

( E q u a t i o n s 2 a n d 3 ). Co(EDTA)- + Co(NH ) + 3

The metric

6

3

+

3NH GH GH S2

unsymmetrical w i t h the

Co(NH CH CH S)

2

2

3NH CH CH S-

isomerism among

expected

2

square

2

2

nature

2

of

its m e t a l

2

2

Go(NH GH GH S) 2

2

2

β-mercaptoethylamine complexes,

p l a n a r n i c k e l (II)

+

3

cis

3

E D T A +

6NH

should

a n d trans

(2)

4

(3)

3

lead

isomers

a n d p a l l a d i u m ( II )

facial a n d p e r i p h e r a l isomers w i t h cobalt (III).

-

to

geo

might

derivatives

However, during

the

be and

course

of

the preparation of various samples i n w h i c h the p r o c e d u r e a n d experimental con ditions w e r e v a r i e d , n o e v i d e n c e of s u c h i s o m e r i s m w a s a p p a r e n t is p a r t i c u l a r l y e v i d e n t i n t h e c a s e o f t h e c o b a l t ( I I I ) p a r e d b y the a d d i t i o n of c o b a l t (II)

complex, C o L .

chloride 6-hydrate

3

(6,

15).

to s t r o n g l y b a s i c

solution of the l i g a n d a n d b y d i s p l a c e m e n t o f a m m o n i a a n d

This

Samples pre aqueous

(ethylenedinitrilo)-

In Reactions of Coordinated Ligands; Busch, D.; Advances in Chemistry; American Chemical Society: Washington, DC, 1962.

Metal Complexes of

BUSCH ET AL.

127

β-Mercaptoamines

tetraacetate f r o m the c o r r e s p o n d i n g c o m p l e x e s w e r e f o u n d to h a v e i n d i s t i n g u i s h able infrared spectra a n d identical p h y s i c a l properties

( 6 ).

T h e methods usually

e m p l o y e d i n the s e p a r a t i o n of g e o m e t r i c a l isomers are e x p e r i m e n t a l l y i m p r a c t i c a l in

v i e w of the

suggested mutual

(6,

cis

very

coordination

sphere.

This

and

symmetry

the

slight solubilities of

the

uncharged

that the k n o w n isomers of M L

15)

of

is c o n s i s t e n t of the

all

the

mercaptide

functions

w i t h the

pi-bonding

tendencies

appropriate

central

atom

2

and M L

2

I n his early observations

3

Jensen


reported

(15)

ligand.

the

in

the

this

2

f o r m a t i o n of

material

by

2

2

complexes

a

second

of

X

where

reveals

and

2

nickel(II)

two

methods

Co(NH CH 2

that the three n i c k e l (II)

derivative

of

that that

NH CH CH S; 3

2

2

Jicha and Busch

measured

a

number

is C I , B r ,

o r I.

T h e molar magnetic

of

also b e e n

atoms

are

2

all diamagnetic

obtained, b y

the

2

Structure

II

l e d to

the

assignment

is a s i m p l i f i e d

a n d , therefore,

•CH

CHÎ

2

of

continuous

of structure

I

of the

to

this

same

(Table

II). for

\

.NH

CH

:

\

N

/

\

s

/

s

\

2

x

CH

requires structure

the

cis o r i e n t a t i o n o f t h e

2

2

2

2

Ni

t w II o sulfur atoms

in N i L .

O n the

2

2

2

2

2

2

+ Ni^

2

bis species

+

2

of

from

[Ni { N i ( N H C H C H S ) ) ] 2

p r e p a r a t i o n of the t r i n u c l e a r n i c k e l (II)

uncharged

basis 2

(Equation 4).

2

2Ni(NH CH CH S)

I

2

I, p r o c e d u r e s h a v e b e e n d e v i s e d f o r t h e s y n t h e s i s o f N i ( N i L )

the neutral bis complex, N i L

The

Ni

ion.

Structure

N

Cl .Ni

These

novel complex

substance.

^ N H 2

pre

variations,

Cl

CH -CH

I)

S o l u t i o n s o f t h e salts i n w a t e r

method

representation

2

(Table

t h e e x i s t e n c e o f m a t e r i a l s o f t h e s a m e c o m p o s i t i o n i n d i l u t e s o l u t i o n s (16). considerations

its

(NH CH CH -

3

susceptibility

b e h a v e as u n i - d i v a l e n t e l e c t r o l y t e s , as i n d i c a t e d b y m o l a r c o n d u c t a n c e has

2

Jensen suggested

zwitter ion,

and

sumably coordinated i n a square planar fashion. Evidence

con

β-mercaptoethylamine,

d i f f e r e n t salts, a l l o f w h i c h d i s p l a y t h e u n u s u a l s t o i c h i o m e t r y , N i 2

atoms

This

T h i s d a r k g r e e n solid has b e e n isolated i n the f o r m of three

S) X , 4

donor

(6).

h o w e v e r , h e o f f e r e d n o e v i d e n c e i n s u p p o r t of this c o n t e n t i o n . prepared

with

coordination

of the

M(NH CH CH S )

o n the

the l i g a n d m i g h t b e c o o r d i n a t e d i n the f o r m of the (16)

been

a n d p r o p e r t i e s of the tri-

T h i s w a s i s o l a t e d as g r e e n , w a t e r - s o l u b l e c r y s t a l s .

physical properties.

has

.

3

Trinuclear Cations D e r i v e d from CH S) .

It

are associated

3

orbitals

d

clusion p r o v i d e s a r e a d y explanation for the structures n u c l e a r derivatives of M L

species.

and C o L

2

w i t h n i c k e l (II)

i o n has

2

2

2

(4)

2

c o m p l e x b y s o l u b i l i z a t i o n of the been

generalized b y


the

use

of


128 Table I.

Molar Susceptibilities' and Magnetic Moments of Complexes of β-Mercaptoethylamine 1

Mfiff.

Compound [Ni(NH CH CH S) ] [Co(NH CH CH S) l [ N i { N i ( N H G H G H S ) } ,1 G l [Ni | N i ( N H , C H , C H » S ) 1 2 I B r [Ni f N i ( N H G H G H S ) 1 ] 1 [Pd { N i ( N H C H C H S Ï } 1 G l [ G u ( I I ) { N i ( N H G H G H S ) } 2I G l [Gu(T) { N i ( N H G H G H S ) } ,1 G l [Gd { N i ( N H C H C H S y [GdGl ] [Hg { N i ( N H G H G H S ) [ H g { N i ( N H C H C H S ) 2I [ H g B r ] [ H ^ { N i ( N H G H G H S ) 2I [ H g l ] [ G d { N i ( N H G H G H S ) 2] [ H g l ] [Ni{Pd(NH GH GH S) ] ]C1 -2H 0 [Go(Co(NH GH GH S) ]G1 [ G o ( G o ( N H G H G H S ) 2Br [ N i { G o ( N H G H G H S ) : 2] B r 2

2

2

2

2

2

2

2

3

2

2

2

2

2

2

2

2

2

2

2

2

2

4

2

2

2

2

2

2

2

2

2

2

2

4

2

2

4

2

2

2

2

2

2

2

2

3

2

4

2

2

2

2

2

2

2

2

2

2

2

2

2

2

2

2

2

2


2

2

2

2

2

2

2

2

2

2

2

2

3

3

2

χ X 70-e {Complex)

T,° K.

-98.7 -55.4 -339.0 -282.2 -205.4 -86.9 +452.1 -75.9 -291.9 +6732.0 + 5938.4 -474.1 -216.3 -142.1 +7324.9 -118.8 + 3983.6

300 300 300 305 305 302 305 305 303 305 305 302 305 302 304 303 303

(B.M.) per Metal Ion

03

95 79

49 23

M o l a r susceptibilities of l i g a n d a n d anions (using Pascal's constants). NH GH GH S -50.13 X 1 0 - 6 ; ·α~, - 2 0 . 1 X 1 0 - · ; { B r " - 3 0 . 6 X 1 0 " » ; I~, - 4 4 . 6 X 1 0 - 6 0

2

Table II.

Τ =

25° G. \,

2

2

2

2

2

2

2

2

2

2

2

2

2

2

2

2

2

2

2

2

2

2

2

2

2

2

2

2

2

2

2

2

2

2

2

2

2

2

2

2

2

2

2

2

2

2

2

2

2

2

2

2

2

2

2

2

2

2

2

4

2

2

4

î

2

2

2

3

2

2

2

1

242 245 246 244 184 238 238 258 127 442 423 148 362 231

2

2

2

2

2

2

2

Ohm

m

[Ni { N i ( N H G H G H S ) j ] G 1 [ N i ( N i ( N H G H G H S ) 2] B r [Ni { N i ( N H C H C H S ) ]I [ P d { N i ( N H G H G H S ) } 2] G l [Gu(II) { N i ( N H G H G H S ) 1 ] C l [Pt { N i ( N H G H G H S ) ) ] G l [ P d ( P d ( N H G H G H S ) } ]G1 [Ni{Pd(NH GH GH S) ]C1 -2H 0 [Gu(I) f N i ( N H G H G H S ) } ] G l [Gd { N i ( N H G H G H S ) } ] [ G d G l ] [Gd f C d ( N H C H C H S ) (,] [ G d G l ] [ C o { C o ( N H G H G H S ) } 2I G l [ C o f C o ( N H C H C H S ) ! ]Br [ N i { G o ( N H G H G H S ) } ]Br 3

2

M o l a r conductance determined i n m e t h a n o l .

solutions of other divalent a n d m o n o v a l e n t substantial array of trinuclear

complexes

m e t a l i o n s as s o l u b i l i z i n g m e d i a .

ions c o n t a i n i n g m o r e

w i t h the mercaptide

been combined b y bridge formation with P d ( I I ) , C u ( I I ) , Pt(II).

I a n d II.

T h e molar

susceptibilities

of the resultant

T y p i c a l equations

Continuous

variation

(17).

Complex

t h a n o n e k i n d of m e t a l i o n are relatively rare, despite the

strong b r i d g e - f o r m i n g tendency associated

conductances

A

containing t w o different metal ions has

b e e n isolated i n the course of s u c h studies b y J i c h a a n d B u s c h

and

2

Molar Conductances of Complexes of β-Mercaptoethylamine Compound

0

2

studies

a n d magnetic

polymetallic complexes

moments

been

particularly

NiL

2

has

Cd(II),

a n d the

molar

are s u m m a r i z e d i n Tables

f o r the f o r m a t i o n of s u c h species have

group.

Cu(I), Hg(II),

revealing

are g i v e n b e l o w . i n these

systems,

since they show, f o r example, that 1 m o l e of P d ( I I ) combines w i t h 2 moles of N i L in dilute solution.

2

T h i s r e s u l t o b v i a t e s t h e p o s s i b i l i t y t h a t t h e t r i n u c l e a r s p e c i e s is


BUSCH ET AL. limited

Metal Complexes of

in existence

to t h e

s o l i d state.

2[Ni(NH CH CH S) ] 2

2

2[Ni(NH GH GH S) ] 2

2

2

2

2

+

(M

+

2

M+

M'C1 ~ 4

=

Cd+

->

-*

2

or G u

2

T h e magnetic

2

129

β-Mercaptoamines moments

and molar

[M {Ni(NH CH CH S) ] 2

2

2

2

[M |Ni(NH GH GH S) | ] ^ ,

+ 2

;

2

M ' =

Pd

2

2

or P t

+ 2

2

+ 2

structures

p r o p o s e d , w i t h the

single exception

rivatives i n w h i c h it m u s t b e p r e s u m e d that the

2

2

of the

Hg(II)

4G1~

(6)

) 2

the

(5) +

2

d u c t a n c e s of the p u r e substances of the c o m p o s i t i o n [ M ( N i L ) ] + with

con-

+ 2

are

consistent

m e r c u r y (II)

i o n impairs the

de

donor

a b i l i t y o f t h e m e r c a p t i d e f u n c t i o n to t h e e x t e n t t h a t i t n o l o n g e r c a u s e s s p i n p a i r i n g in the m i x e d m e t a l d e r i v a t i v e w i t h N i ( I I ) . As form

t h e d a t a s u m m a r i z e d i n T a b l e s I a n d II s h o w , b o t h P d ( I I )

homometallic trinuclear

Also, the

mononuclear Pd(II)


trinuclear species—e.g., The also

complexes

of

the

general

2

c o m p l e x h a s b e e n u t i l i z e d to f o r m 2

demonstrated

[M(CoL )]X , 3

2

(6).

2

2

Two

w h e r e M is N i ( I I )

n

2

heterometallic

[Ni(PdL ) ]X .

b r i d g e - f o r m i n g p r o c l i v i t y of the n e u t r a l c o b a l t (III)

been

a n d C o (II)

structure[M ( M L ) ] X .

D e t a i l e d s t u d y of these substances

trinuclear

complex, C o L ,

has

3

compounds

of

the

formula

or C o ( I I I ) , h a v e b e e n isolated i n p u r e f o r m . indicates that the complex

CoL

3

forms

three

m e r c a p t i d e b r i d g e s to the t h i r d m e t a l i o n , thus p r o v i d i n g o c t a h e d r a l c o o r d i n a t i o n o f t h e six s u l f u r a t o m s a b o u t t h a t i o n .

D a t a o n these u n u s u a l c o m p o u n d s are

also

i n c l u d e d i n T a b l e s I a n d II.

Complexes of Methyl-2,2'-dimercaptodiethylamine. ill),

a n d c o b a l t (II)

f o r m stable complexes

2,2'-dimercaptodiethylamine.

These

metal

Bis

(II),

ion per Ni L , 2

structure

ligand

was

2

anion.

first

N i c k e l (II),

palladium-

i n ammoniacal solution w i t h methyl-

compounds

exhibit a

stoichiometry

of

one

(methyl-2,2 -dimercaptodiethylamine) dinickelr

prepared by Harley-Mason

(12),

who proposed a

dimeric

( s t r u c t u r e s III a n d I V ) f o r t h i s n o n e l e c t r o l y t e o n t h e b a s i s o f its m o l e c u

l a r w e i g h t as d e t e r m i n e d c r y o s c o p i c a l l y i n e t h y l e n e d i b r o m i d e . compound, methanol,

prepared were

in agreement

found

by

Harley-Mason's

b y Jicha

and

procedure

Busch

(18)

w i t h the p r o p o s e d structure.

to

and be

S a m p l e s of

recrystallized

essentially

this from

diamagnetic,

F u r t h e r , the later investigators

point

,CH CH; 2

\ CH CH ' 2

CH,

2

III

IV

out that the usual p y r a m i d a l structure

of t h r e e c o v a l e n t s u l f u r ( I I )

suggests

the c o o r d i n a t i o n spheres of the t w o m e t a l ions w i l l not be coplanar. to a V - s h a p e d c o n f i g u r a t i o n f o r t h e a m i x t u r e of o p t i c a l a n t i p o d e s . water

and

soluble i n halogenated

chloroethylene,

and

captodiethylamine )

ethylene

m o l e c u l e a n d the

The compound N i L 2

solvents

dibromide.

such

substance

2

and

ligand.

T h i s substance

exist

as

chloroform, b r o m o f o r m , triblis(methyl-2,2'-dimer-

can be prepared from aqueous

m o n i a s o l u t i o n u s i n g s t o i c h i o m e t r i c q u a n t i t i e s of p o t a s s i u m n i c k e l (II)

should

that leads

is o n l y s l i g h t l y s o l u b l e i n

Yellow-orange

dipalladium(II), P d L , 2

as

2

This

am

tetrachloropalladate(II)

bears a v e r y close r e s e m b l a n c e

to t h e c o r r e s p o n d i n g

c o m p l e x i n its p h y s i c a l p r o p e r t i e s a n d s t r u c t u r e .



130

Complexes of 2,2'-Dialkyl(ethanediylidenedinitrilo)diethanethiols. viously

u n k n o w n Schiff base

derivatives

of

α-diketones

with

a m i n e s s h o u l d b e i d e a l l y s u i t e d to f o r m m e t a l c o m p l e x e s coordinated in a planar tetradentate manner.

Further,

T h e pre

β-mercaptoalkyl-

i n w h i c h the

l i g a n d is

the m e r c a p t i d e

functions

s h o u l d o c c u p y cis p o s i t i o n s i n t h e c o o r d i n a t i o n s p h e r e o f t h e m e t a l i o n . V

illustrates

the

structure expected

for s u c h substances.

Structure

Three products

might

CH2CH2,

\

C H C H L2 2

:


V be

expected

from

the

reaction

of

an

α-diketone

with

a

mercaptoamine:

the

Schiff base, the thiazoline, a n d the mercaptal.

M e r c a p t a l s h a v e b e e n f o u n d to

of n o significance u n d e r the

reactions

tories the

c o n d i t i o n s of the

Thiazolines, however,

(23).

d o m i n a n t p r o d u c t s , as

o-aminobenzenethiol.

In

found, similar

reactions

with

h a v e s h o w n that the a d d i t i o n of n i c k e l (II) greatly

improves

i n the

reaction

to

of b i a c e t y l

β-mercaptoethylamine,

yield.

be

labora

f o r m r e a d i l y i n all cases a n d a p p e a r

for example,

lines are n o r m a l l y f o r m e d i n greater t h a n 5 0 % condensation

s t u d i e d i n these

be

with

thiazo

Thompson and Busch

(23)

acetate shortly after initiation of

yields of the

desired

Schiff base.

Under

the

these

c o n d i t i o n s , t h e S c h i f f b a s e w a s i s o l a t e d i n t h e f o r m o f its c o m p l e x w i t h n i c k e l ( I I ) ion.

T h i s r e a c t i o n p r o v i d e s a d r a m a t i c e x a m p l e of the role p l a y e d b y a m e t a l i o n

i n f a c i l i t a t i n g t h e f o r m a t i o n o f a n o r g a n i c m o l e c u l e t h a t is o t h e r w i s e s t r o n g l y d i s c r i m i n a t e d against

b y c o m p e t i n g reactions.

I n effect,

the

metal

ion brings

the

r e a c t a n t s t o g e t h e r i n t h e p r o d u c t f o r m t h a t is m o s t f a v o r a b l e f o r c o m p l e x a t i o n . T h e p r o c e d u r e o f T h o m p s o n a n d B u s c h (23)

has resulted i n the synthesis

2 , 2 ' - d i m e t h y l ( e t h a n e d i y l i d e n e d i n i t r i l o ) d i e t h a n e t h i o l o n i c k e l ( II ) ,

Ni(B E ) ;

of 2-

m e t h y l - 2 - e t h y l ( e t h a n e d i y l i d e n e d i n i t r i l o ) d i e t h a n e t h i o l o n i c k e l ( II ), N i ( Ρ Ε ) ; a n d 2,

m e t h y l - 2 ' - p e n t y l ( e t h a n e d i y l i d e n e d i n i t r i l o ) d i e t h a n e t h i o l o n i c k e l ( II ) , yields of 70

to 7 8 % .

T h e magnetic

moments

e x p e c t e d p l a n a r c o o r d i n a t i o n of the N i (II)

of these c o m p l e x e s

ion.

Ni(O E )

in

all confirm

Molecular weight

the

determinations

h a v e s h o w n t h e s u b s t a n c e s to b e m o n o m e r i c i n d i c h l o r o e t h y l e n e , w h i l e i n f r a r e d d a t a a n d total elemental analyses plexes to

are

highly

transmitted

colored,

light.

They

further support the appearing exhibit

nitrobenzene, a n d bromobenzene. vary

strongly

benzene

from

solvent

to

to

considerable

assigned structures.

The

reflected

red-brown

light

and

solubilities i n water,

com

acetone,

T h e colors of the solutions of these c o m p o u n d s

solvent,

to r e d - b r o w n i n w a t e r .

green

generally

T h e color

ranging

from

in pyridine more

that i n b e n z e n e a n d i n c h l o r o f o r m than that i n water.

violet-purple in nearly

resembles

In v i e w of the fact

that

p y r i d i n e is t h e s t r o n g e s t c o o r d i n a t i n g a g e n t a m o n g t h e s e s o l v e n t s , w h i l e c h l o r o f o r m a n d b e n z e n e a r e a m o n g t h e w e a k e r , it w a s c o n c l u d e d t h a t this e f f e c t o n t h e c h a r g e t r a n s f e r s p e c t r u m is n o t a s s o c i a t e d n u m b e r of the n i c k e l (II)

ion.

Reaction of Coordinated

Mercaptide

w i t h the e x p a n s i o n of the

Group with Alkyl

coordination

Halides

E a r l y o b s e r v a t i o n s r e g a r d i n g r e a c t i o n s o f t h i s class w e r e m a d e b y E w e n s Gibson

(8),

and

w h o s t u d i e d the reaction of ( β - m e r c a p t o e t h y l a m i n e ) d i e t h y l g o l d ( I I I )


BUSCH ET AL.

Metal Complexes of

131

β-Mercaptoamines


with methyl iodide and ethyl bromide. This novel and interesting example of an addition reaction occurring without destruction of the complex was complicated by the formation of oils, and pure compounds could be isolated as solids only in the form of picrate salts. The synthesis of a large number of metal complexes of mercaptoamines by Busch and coworkers (6, 15, 17, 24) has opened the way for detailed study of the reactions of the coordinated mercaptide function. Mercaptoamine complexes provide the first extensive series of complexes of k n o w n structure i n w h i c h the effect of varying structural parameters on the reactivity of the mercaptide group can be subjected to investigation. Synthesis of S-Alkyl-^-mercaptoethylamine Complexes b y A l k y l a t i o n of βMercaptoethylamine Compounds. Jicha and Busch (18) have reported studies on the reactions of the nickel (II) and palladium (II) complexes of β-mercaptoethylamine w i t h methyl iodide and benzyl halides. Superficially, the most typi cal of these experiments were concerned w i t h the reactions of bis(/?-mercaptoethylamine)-nickel (II) w i t h alkyl halides in dimethylformamide as the solvent. Despite the unfavorable solubility of the nickel (II) complex i n dimethylform amide, the alkylation reactions have been observed to proceed at room tempera ture, resulting i n dissolution of the complex. In the case of methyl iodide, the reaction proceeds to completion i n approximately 2 hours, during w h i c h time the color of the solution undergoes a gradual change from a deep red to an emerald green. The ready solubility of the product i n dimethylformamide facilitates the separation of the final product from the unreacted starting material. Bemoval of the dimethylformamide i n vacuo produces a green oil w h i c h can be induced to crystallize upon the addition of cold absolute ethanol, yielding a light green solid. Analysis of the solid from the reaction of the nickel (II) complex N i L w i t h methyl iodide reveals a stoichiometry of 1 nickel(II) : 2 N H C H C H S — C H : 2 iodides. The infrared spectrum displays two sharp bands of m e d i u m intensity at 3263 and 3216 c m . , w h i c h are characteristic of the — N H asymmetric and sym metric stretching frequencies. A third band of comparable intensity occurs at 1578 c m . - w i t h a shoulder at 1588 c m . - , w h i c h can be attributed to the — N H deformation mode. The appearance of these bands confirms the presence of a primary amine. O n the basis of these spectral observations, the electrophilic nature of the attacking alkyl group, and the usual inability of the coordinated amine-nitrogen to undergo chemical reactions (4, 5 ) , methylation of the ligand is presumed to occur at the coordinated sulfur atom (Equation 7 ) . The alkylation 2

2

- 1

2

2

3

2

1

1

[Ni(NH CH CH S) ] 2

2

2

2

+

2CH I

D M

3

2

*>

[Ni(NH CH CH SCH ) l2] 2

2

2

3

(7)

2

of [ N i ( N H C H C H S ) ] was also carried out using benzyl halides under the same conditions, and the dibenzylated products were isolated. 2

2

2

2

[Ni(NH CH CH S) ] 2

2

2

2

+

2C H*CH X 6

2

[Ni(NH CH CH S—CH C H 2

2

2

2

e

f i

) X ] 2

(8)

2

where X = C l - , Br—, or I—. In these cases, the rate of alkylation might be expected to be dependent upon the particular benzyl halide used. Indeed, a significant variation was observed, w i t h the rate of benzylation increasing i n the order: C H C H C 1 < C H C H B r < C„H CH I. ( ;

B

5

2

G

5

2

2

The

reaction

of tetrakis(/?-mercaptoethylamine)trinickel(II)

iodide, [ N i -

j N i ( N H C H C H S ) } o ] I , with methyl iodide was found to result i n the forma2

2

2

2

2


132


t i o n o f a p r o d u c t w h i c h is i d e n t i c a l to t h a t o b t a i n e d b y m e t h y l a t i o n o f CH CH S) ] 2

2

(Equation

2

[NijNi(NH GH GH S) i2]l2 2

2

+

2

2

3

2

2

3

2

reaction

without

( N H C H C H S - C H C H ) C 1 ] 2

2

2

2

6

5

2

apparent

and

2

+ Nils

2

I n this c a s e t h e g r e a t e r s o l u b i l i t y o f t h e t r i m e r i c c o m p l e x a smoother

2

4GH I

2[Ni(NH GH GH S—GH ) l2]

proiuces

[Ni(NH -

9).

(9)

in dimethylformamide

contamination.

Similarly,

[Ni-

[ N i ( N H C H C H S - C H C H ) B r ]

can

2

2

2

2

6

5

2

2

b e p r e p a r e d b y r e a c t i n g t h e c h l o r i d e a n d b r o m i d e salts o f t h e t r i m e r i c c o m p l e x w i t h benzyl chloride a n d benzyl bromide, respectively. m i d e salts o f t h e

trimeric species

are

However, chloride and

bro-

c o n s i d e r a b l y less s o l u b l e i n D M F t h a n

is


the c o r r e s p o n d i n g iodide. The

observations

reported

above

o n the

alkylation of the

on

of

CH S) ]

is t r e a t e d w i t h a l k y l h a l i d e s , t h e t r i m e r i c c o m p l e x f o r m s i n s o l u t i o n a n d

2

2

the

neutral

2

2

2

2

important

complex

reaction

2

an

bearing

[Ni { N i ( N H C H C H S ) } ] + , 2

have

trimeric

species,

complex,"* [ N i ( N H C H C H S ) ] . 2

2

c a n b e i s o l a t e d i f t h e r e a c t i o n is i n t e r r u p t e d .

2

When

2

T h e appearance

stable intermediate indicates that the alkylation reaction of p r o c e e d s i n a s t e p w i s e f a s h i o n ( E q u a t i o n s 10 to [Ni(NH CH CH S) ] 2

2

2

[Ni(NH CH CH S—R) X ] 2

2

2

2

+

2

+

2

2RX

2

2

2

2

2

The the

first

+

2

2

2

2

2

+

2

bis

\

2

2

2NH GH GH SR 2

2

complex

[Ni(NH CH CH S) ] 2

2

2

is

2

(10)

2

2

2

2

+ Ni^ +

more

2

2

2

2

i n solution.

strongly

According

coordinated

tion of [ N i { N i ( N H C H C H S ) } ] + . 2

2

small amount

of

Equation

than

11,

N H C H 2

2

shown—i.e., forma-

T h e excess a l k y l a t i n g a g e n t t h e n

2

2

(13)

2

to

ligand

2

2

(12)

[Ni(NH GH GH S—R) X ]

2

w h i c h is

a

(11)

2

2X~

2

2

C H S — R , a r e l a t i o n s h i p l e a d i n g to the d i s p l a c e m e n t reactions 2

2

2NH GH GH S—R

s t e p m i g h t b e c o n s i d e r e d to i n v o l v e a l k y l a t i o n o f t h e

uncharged

2

4RX

2

2

2X-

2

2

2[Ni(NH GH GH S—R) X ] +

2

2[Ni(NH9CH GH S) ]

[Ni!Ni(NHoCH CH S) ! ]X, +

Ni+

o f t h i s s p e c i e s as a

[Ni(NH CH CH S) ]

2

\

2

2

[Ni(NH GH GH S—R) X ]

2

2

2

13).

[Ni(Ni(NH GH GH S) ! ]X 2

the

[Ni(NH CH -

attacks

t h e s o l u b l e t r i m e r i c s p e c i e s , l e a d i n g to t h e f o r m a t i o n o f t h e o b s e r v e d p r o d u c t

as

s h o w n i n E q u a t i o n s 12 a n d 1 3 . A n alternative process i n v o l v i n g the direct a l k y l a t i o n of [ N i ( N H C H C H S ) 2

m i g h t also b e s u g g e s t e d

( i n p l a c e of E q u a t i o n 12).

ciated with an equilibrium between complex particular

in solution. species

the trimeric species

O n the basis of the

w h i c h undergoes

2

2

T h i s possibility m a y be a n d the

evidence presented

a l k y l a t i o n is s t i l l s o m e w h a t

2

]

asso-

uncharged

bis

at t h i s p o i n t ,

the

in doubt.

The

i s o l a t i o n o f t h e a l k y l a t e d c o m p l e x e s i n y i e l d s g r e a t e r t h a n 6 6 . 6 7 % is i n d i c a t i v e o f complex

formation between

the

s o l v a t e d n i c k e l (II)

ions a n d the

l i g a n d f o r m e d d u r i n g t h e r e a c t i o n (as i n d i c a t e d b y E q u a t i o n

free

alkylated

13).

T h e solid products obtained using m e t h y l iodide a n d b e n z y l iodide exhibit m a g n e t i c m o m e n t s of 3.18 magnetic

moments

structures i n v o l v i n g

a n d 3.09

correspond

to

Bohr magnetons, values

t y p i c a l of

octahedral nickel (II). 2

2

3

2

2

These

(18).

u n p a i r e d electrons

in

C o n s e q u e n t l y , these c o m p o u n d s

f o r m u l a t e d as [ N i ( N H C H C H S - C H ) I ] a n d 2

respectively two

are

[ N i ( N H C H C H S - C H C H ) 2

2

2


2

6

5

2

BUSCH ET AL. I ].

133

Metai Complexes of β-Mercaptoamines

T h e substantial solubilities of these c o m p o u n d s i n c h l o r o f o r m a n d other

2

p o l a r o r g a n i c solvents are i n a g r e e m e n t

w i t h t h e i r f o r m u l a t i o n as

I n m e t h a n o l at 2 5 ° C , t h e m o l a r c o n d u c t i v i t i e s o f 1 6 6 ( N H C H C H S - C H ) I ] 2

2

2

3

2

and

2

a n d 167

o h m

[Ni(NH CH CH S-CH C H ) I ], 2

2

2

2

6

5

2

less

nonelectrolytes. -

for [ N i -

1

respectively,

2

are c h a r a c t e r i s t i c o f d i - u n i v a l e n t e l e c t r o l y t e s i n t h i s s o l v e n t , i n d i c a t i n g a l m o s t c o m plete

polar

solvent.

D e c o m p o s i t i o n of these complexes was o b s e r v e d u p o n dissolving i n water.

solvolysis of

the

coordinated

i o d i d e ions

i n this

relatively

Visible

a n d n e a r - i n f r a r e d s p e c t r a results are also c o n s i s t e n t w i t h structure V I . X


R

R

X VI

Alkylation S) ],

of the

uncharged

bispalladium(II)

complex,

[Pd(NH CH CH 2

2

proceeds s o m e w h a t differently u n d e r the conditions e m p l o y e d for the

2

sponding nickel(II)

complex.

Allowing

the

h o u r s at s l i g h t l y a b o v e r o o m t e m p e r a t u r e

reaction

mixture

to

stir f o r

2

corre several

results i n the f o r m a t i o n of a r e d

solu

tion, w h i c h u p o n concentration a n d the a d d i t i o n of c o l d ethanol yields a r e d solid h a v i n g a s t o i c h i o m e t r y o f 1 P d ( I I ) :1 N H

C H

2

2

C H

2

S - C H

is o n l y s l i g h t l y s o l u b l e i n e t h a n o l a n d c h l o r o f o r m . warm

ethanol w i t h no

apparent

p o u n d as t h e n o n e l e c t r o l y t e , these solubility properties

decomposition.

3

: 2 I - .

T h e f o r m u l a t i o n of this

[Pd(NH CH CH S—CH )I ], 2

a n d the

2

This compound

It c a n b e r e c r y s t a l l i z e d f r o m

2

3

com

is i n a g r e e m e n t

2

c o o r d i n a t i o n n u m b e r of 4

with

for p a l l a d i u m ( II).

T h e e a s e o f f o r m a t i o n o f t h e m o n o a l k y l a t e d c o m p l e x is a l s o d e p e n d e n t u p o n particular alkyl halide employed. CH CH S) ] 2

2

2

T h e reaction of b e n z y l b r o m i d e w i t h

2

6

5

2

r e s u l t e d i n the i s o l a t i o n of a s o l i d h a v i n g a c o m p o s i t i o n s u g g e s t i v e of

a m i x t u r e of [ P d ( N H C H C H S - C H C H ) ] B r C H )Br ].

the

[Pd(NH -

2

2

2

6

5

2

2

and

[ P d ( N H

2

C H

2

C H

2

S - C H

2

-

T h i s b e h a v i o r is i n a c c o r d w i t h t h e l e s s e r c o o r d i n a t i n g a b i l i t y [ t o w a r d

2

p a l l a d i u m ( II ) ] o f b r o m i d e i o n as c o m p a r e d to i o d i d e i o n . E x p e r i m e n t s h a v e s h o w n that these complexes w i l l react w i t h d i h a l o g e n c o m p o u n d s to f o r m n e w c h e l a t e r i n g s , c o n v e r t i n g t w o b i d e n t a t e l i g a n d s i n t o a s i n g l e t e t r a d e n t a t e l i g a n d in situ. tion b e t w e e n dentate

NiL

ligand

bromide.

I d e n t i c a l p r o d u c t s are o b t a i n e d f r o m the l i g a n d r e a c

and α,αί'-dibromo-o-xylene,

2

and then

forming

the

complex

2

2

2

4

2

2

The

magnetic

a r e v e r y c l o s e to t h e v a l u e o f 3 B o h r m a g n e t o n s , containing

first

p r e p a r i n g the

tetra

a n d n i c k e l (II)

B o t h p r o d u c t s w e r e i s o l a t e d as l i g h t b l u e p o w d e r s o f t h e c o m p o s i t i o n

Ni(NH CH CH S) .CoH (CH Br) . 2

and by

f r o m that l i g a n d

octahedral

nickel (II).

of

the

materials

w h i c h is e x p e c t e d

for

structures

T h e latter result

moments

i m p l i e s c o o r d i n a t i o n of

the

b r o m i d e i o n s to t h e n i c k e l a t o m , i n a d d i t i o n to t e t r a d e n t a t e c o o r d i n a t i o n b y

the

organic ligand. The

use

of

d i m e t h y l f o r m a m i d e as

merits further discussion.

m e d i u m i n these

reactions

I n v i e w of the ease of d i s s o l u t i o n of m a n y

inorganic

salts i n t h i s s o l v e n t at r o o m t e m p e r a t u r e ,

the

solvent

the a p p a r e n t success e n c o u n t e r e d i n the

a l k y l a t i o n of the c o o r d i n a t e d s u l f u r a t o m i n [ N i ( N H C H C H S ) ] 2

2

the solubility of the intermediate [ N i { N i ( N H C H C H S ) } 2

reaction.

Moreover, Kornblum

and Blackwood

2

2

(19)

2

2

2

]X

have

2

2

m a y arise f r o m

f o r m e d during the

reported

that

under

c o n d i t i o n s s i m i l a r to t h o s e e m p l o y e d f o r t h e a b o v e r e a c t i o n s , d i m e t h y l f o r m a m i d e a l s o u n d e r g o e s a l k y l a t i o n ; h o w e v e r , s u c h r e a c t i o n s a r e r e p o r t e d to b e s l o w , a n d i n



134 the

case of 0 . 2 M

solutions of m e t h y l i o d i d e a n d

benzyl bromide in dimethyl

f o r m a m i d e at 2 5 ° to 3 0 ° C , t h e r e a c t i o n is o n l y 1 0 % days, respectively.

Interference

c o m p l e t e a f t e r 12

b y this s o l v e n t r e a c t i o n

and

19

is o b v i a t e d i n v i e w

of

the m o r e r a p i d a l k y l a t i o n of the c o o r d i n a t e d s u l f u r a t o m .

Synthesis of S-Alkyl-IV-methyl^^'-dimercaptodiethylamine by Direct Alkyla tion of Complexes M L . T h e n i c k e l ( I I ) a n d p a l l a d i u m ( I I ) c o m p l e x e s of 2

2

methyl^-^'-dimercaptodiethylamine, [M

{ C H N ( C H C H S ) } ] , exhibit a similar

2

3

2

2

2

2

t e n d e n c y to u n d e r g o r e a c t i o n w i t h m e t h y l i o d i d e a n d b e n z y l b r o m i d e (18).

The

extreme solubilities of these complexes i n c h l o r o f o r m a l l o w the a l k y l a t i o n reaction to

be

conducted

homogeneously.

In

the

case

of

[Ni {CH N-(CH CH S) } ], 2

3

2

only one chloroform-soluble p r o d u c t has b e e n isolated, regardless

2

of the

2

2

quantity

of m e t h y l i o d i d e or b e n z y l b r o m i d e u s e d .

T h e red-brown methylated

derivative

and

be

degree

the

b r o w n benzylated derivative can

isolated w i t h a certain

of

difficulty after c o n c e n t r a t i o n of the respective c h l o r o f o r m solutions a n d trituration


with c o l d absolute ethanol a n d benzene. A n a l y t i c a l d a t a o n t h e s o l u b l e p r o d u c t s i s o l a t e d f r o m c h l o r o f o r m are i n e x c e l lent agreement Br .

w i t h the c o m p o s i t i o n :

T h e magnetic

-

B o h r m a g n e t o n s p e r n i c k e l ( II ) . benzylated complexes tively.

(structure V I I ) lead

monoalkylated ligand:1

the

or

-

1.89

T h e m o l a r c o n d u c t i v i t i e s of the m e t h y l a t e d

i n m e t h a n o l at 2 5 ° C . are 7 5 . 4

a n d 68.4

ohm

-

1

,

and

respec

for u n i - u n i v a l e n t electrolytes

in

electro

d o e s n o t a p p e a r to b e t o t a l l y c o n s i s t e n t w i t h t h e i r p h y s i c a l

O n e o r b o t h h a l i d e i o n s m a y b e b o u n d to t h e m e t a l i o n . to

I

f o u n d to b e

T h e f o r m u l a t i o n o f t h e s e a l k y l a t e d c o m p o u n d s as d i m e r i c

properties. sults

2

T h e s e values a p p r o x i m a t e those e x p e c t e d

this solvent. lytes

1 Ni+ :1

m o m e n t of this m e t h y l a t e d c o m p l e x w a s

easily

understood

generalization

that

terminal

These

sulfur

re

atoms

alkylate more readily than b r i d g e d mercaptide groups.

^ CH < I CH

Ν

/

CH2CH2

\

S

^ C H

2

Ni

.Ni

2

.CH

2

X

2

a

S'

I

CH2CH2

R

VII

Kinetics and Mechanism of Reactions of Bis ( methyl-2,2'-dimercaptodiethylamine)dinickel(II) with Alkyl Halides. T h e rates o f r e a c t i o n o f [ N i { C H N 2

(CH CH S) } ], 2

ride,

2

2

2

structure

p-chlorobenzyl chloride, and p-nitrobenzyl chloride have

functions

of

measurements

temperature were

and

concentration

in

chloroform

u t i l i z e d to d e t e r m i n e t h e r a t e s .

d u c t e d w i t h excess a l k y l h a l i d e complex).

3

III, w i t h m e t h y l i o d i d e , b e n z y l b r o m i d e , b e n z y l c h l o

J i c h a a n d B u s c h (18)

(20

to

1000

times

been

(3).

studied

A l l experiments the

initial

as

Absorbance were

con

concentration

of

w e r e a b l e to isolate a l k y l a t e d c o m p l e x e s of the

composition

CH2CH2S Ni

2

CH —Ν 3

\

X CH CH SR/ 2

and

2

2

these substances were consequently expected

to b e t h e p r o d u c t s o f t h e

tions u n d e r kinetic investigation.


reac

BUSCH ET AL.

135

Metal Complexes of β-Mercaptoamlnes

S i n c e these reaction

products

exhibit considerable

absorbance

at

the

wave

lengths utilized i n the rate measurements, the c a l c u l a t i o n of rate constants r e q u i r e d a t e c h n i q u e i n c o r p o r a t i n g this factor. successfully.

T w o m e t h o d s of c a l c u l a t i o n w e r e e m p l o y e d

I n s o m e cases, l i m i t i n g a b s o r b a n c e s

(A

)

0 0

were d e t e r m i n e d a n d the

rates w e r e o b t a i n e d f r o m the slopes of g r a p h s of l o g ( A — A

vs.

time.

T h e s e s e r v e d to d e m o n s t r a t e t h e p s e u d o - f i r s t - o r d e r n a t u r e o f t h e r a t e c o n s t a n t ;

how

0

0 0

)/(A—A

)

0 0

ever, the m o r e g e n e r a l c a l c u l a t i o n p r o c e d u r e w a s that d u e to G u g g e n h e i m

(11).

The

was

first-order

d e p e n d e n c e of the rate o n the

concentration

of a l k y l h a l i d e

s h o w n b y v a r y i n g initial concentrations. The

simple second-order

nature

of the

mediate

c o n c l u s i o n s of s o m e c o n s e q u e n c e .

not the

heterolytic

group,

which

b r e a k i n g of a

metal-sulfur b o n d

then might undergo reaction.

e v i d e n c e suggesting consecutive processes


kinetics i n this system T h e rate-determining to

Further,

produce

the

fact

leads to i m

step the

that

is

clearly

free

R - S

there

is

-

no

e l i m i n a t e d the possibility that a n y such

s c h e m e c o u l d e n t e r i n t o t h e t o t a l r a t e e x c e p t e s s e n t i a l l y as a p r e - e q u i l i b r i u m — e . g . , E q u a t i o n s 14 a n d 15.

.S

S Ni

/

\

Ν

S

v

/

Ni

\

N

v

/ S

Ni θ

+

θ

S

. / Ν

\

S

/

/

S

®

S

-f- X ~

(15)

I R

Ν

/ \ Ni

Ni

\

Ν

S

N ^

Ni

RX

. /

\

(M) θ

S

S

x

x

Ni Θ

/

Ν

S

N

/ ' Ni

\

X

.

S—R

I n v i e w o f t h e f a c t t h a t t h e c o m p l e x i n q u e s t i o n is o f t h e d i a m a g n e t i c

inert

class, a s i g n i f i c a n t p r e - e q u i l i b r i u m o f t h i s k i n d is n o t c o n c l u d e d t o b e h i g h l y l i k e l y . C o n s i d e r a t i o n has involving an S 1 N

been

g i v e n to

the

ligand

field

m e c h a n i s m i n the square p l a n a r d

8

case.

i m p l i c a t i o n s of

a

process

A l t h o u g h this p a r t i c u l a r

e x a m p l e h a s n o t p r e v i o u s l y b e e n c a l c u l a t e d , it is r e a d i l y e s t i m a t e d f r o m t h e given b y Basolo a n d Pearson to b e

13.62

Dq.

(1).

T h i s suggests

T h e loss i n s t a b i l i z a t i o n e n e r g y

N

associated

configurations

(d

6

data

estimated

a c o n t r i b u t i o n to the a c t i v a t i o n e n e r g y i n excess

of t h a t e x p e c t e d f o r t h e c o r r e s p o n d i n g S 1 octahedral

is

process i n v o l v i n g e v e n the most

as i n C o + ) . 3

w i t h a loss i n s t a b i l i z a t i o n e n e r g y

T h e c o b a l t (III) of o n l y 4

octahedral

D q . a n d its

inert

case

is

substitution

reactions c o m m o n l y r e v e a l a c t i v a t i o n energies of s o m e 2 0 to 3 0 k c a l . p e r m o l e It is u s u a l l y s u g g e s t e d t h a t s u b s t i t u t i o n r e a c t i o n s i n v o l v i n g i n e r t p l a n a r i o n s

(2). occur

b y the f o r m a t i o n of a d d i t i o n a l b o n d s a b o v e a n d b e l o w the p l a n e of the f o u r o r i g i n a l donor atoms. function.

C h l o r o f o r m is a s s u m e d to b e t o o w e a k a d o n o r m o l e c u l e to s e r v e t h i s

Processes

o f t h i s g e n e r a l t y p e a r e m o r e p r o b a b l e i n s o l v e n t s of g r e a t e r

coordinating ability.



136

It is m u c h m o r e i n k e e p i n g w i t h t h e p r o p e r t i e s o f t h i s r e a c t a n t to p r e s u m e less c o n t r i v e d i n t e r p r e t a t i o n o f t h e r a t e d a t a . b e a s s u m e d to a c t

T h e coordinated sulfur atom

as a n u c l e o p h i l e , d i r e c t l y d i s p l a c i n g t h e

a

may

halide ion from

the

a l k y l h a l i d e , as i l l u s t r a t e d i n E q u a t i o n 16.

Ν

S

\

Ni

/ \

/ V

Ni

/

S,

S,.CH,...I +

CH I

slow

Ni

3

V


+

The

absence

of c o n s e c u t i v e

rate processes

Ni

V

s

/

(16)

\

I"

a l s o justifies t h e

conclusion that

t h e r e a c t i o n o f t h e first m o l e o f a l k y l h a l i d e w i t h t h e c o m p l e x is r e l a t i v e l y s l o w e r t h a n t h e r e a c t i o n o f t h e s e c o n d (k

Reactions of Coordinated Ligands and Homogeneous Catalysis

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