Catalytic Aspects of Metal Phosphine Complexes - American

18 Metal Complexes of Iminophosphine and Iminoarsine Chelating Agents Downloaded by UNIV OF ROCHESTER on September 1, 2017 | http://pubs.acs.org Publication Date: June 1, 1982 | doi: 10.1021/ba-1982-0196.ch018

Structure, Reactivity, and Stereochemistry J O H N E . H O O T S , T H O M A S B.R A U C H F U S S 1 ,and S T E V E N P. S C H M I D T School of Chemical Sciences, University of Illinois, Urbana I L 61801 J O H N C. J E F F E R Y and P A U L A. T U C K E R Research School of Chemistry, The Australian National University, Canberra, The A.C.T., Australia

The coordination chemistry of iminophosphine and im inoarsine ligands is surveyed with emphasis on our re cent results with tetradentate diiminodiarsines and diminodiphosphines derived from 1,2-diaminoalkanes. The ligand en = P prepared from ethylenediamine and o-diphenylphosphinobenzaldehyde forms tetrahedral complexes with copper(I) (X-ray structure) and silver(I), both of which are configurationally labile. The same ligand forms diamagnetic, four- and five-coordinate nickel(II) complexes of the formula [Ni(en = P2)](BF ) and [NiBr(en = P )]Br. Two tridentate en = P com plexes have been prepared, Mo(en = P )(CO) which contains an uncoordinated phosphine moiety, and [Cu(en = P )(t-BuNC)]ClO4 which contains an uncoordi nated imine. Chiral diiminodiarsines prepared from (R)-1,2-diaminopropane and (R,R)-1,2-diaminocyclohexane are uniquely stereospecific in their binding of tetra hedral copper(I) affording complexes in exclusively the Δ(λ) configuration. 2

4 2

2

2

2

3

2

/ C h e l a t i n g phosphine ligands continue to serve coordination c h e m ists i n their efforts to manipulate the electronic a n d reactivity patterns o f metal complexes. These studies have received an a d d i 1To whom correspondence should be addressed. 0065-2393/82/0196-0303$05.00/0 © 1982 American Chemical Society Alyea and Meek; Catalytic Aspects of Metal Phosphine Complexes Advances in Chemistry; American Chemical Society: Washington, DC, 1982.

304

M E T A L PHOSPHINE COMPLEXES

Downloaded by UNIV OF ROCHESTER on September 1, 2017 | http://pubs.acs.org Publication Date: June 1, 1982 | doi: 10.1021/ba-1982-0196.ch018

tional i m p e t u s from the p r o m i s e d a n d sometimes p r o v e n desirable c a t a l y t i c p r o p e r t i e s o f t h e s e c o m p o u n d s . S y n t h e t i c r o u t e s t o m o s t org a n o p h o s p h i n e s r e l y a l m o s t e x c l u s i v e l y o n a P - C b o n d c o u p l i n g as t h e e s s e n t i a l a n d u s u a l l y final s y n t h e t i c s t e p i n t h e i r s y n t h e s i s . O u r i n t e r est i n t h e p h o s p h i n o b e n z a l d e h y d e s s t e m s f r o m t h e p r o s p e c t o f d e v e l o p i n g a l t e r n a t i v e , s y n t h e t i c a l l y m o r e flexible s t r a t e g i e s t o c h e l a t i n g agents b e a r i n g tertiary p h o s p h i n e donors. I m i n e formation, p r o b a b l y the m o s t g e n e r a l l y u s e f u l r o u t e to m u l tidentate l i g a n d s , has b e e n a p p l i e d to the p r e p a r a t i o n o f o n l y a l i m i t e d n u m b e r o f a r s e n i c - ( i ) a n d p h o s p h o r u s - (2, 3) c o n t a i n i n g c h e l a t i n g a g e n t s v i a E q u a t i o n 1. W e h a v e s i n c e d e s c r i b e d t h e a l t e r n a t i v e a n d R E~*NH 2

2

+ R'-CHO

R E~*N==€HR' 2

(1)

m o r e g e n e r a l l y u s e f u l route to this class o f c h e l a t i n g agents v i a E q u a t i o n 2, Ε = P, A s (4). I n a s m u c h as l i n e a r t e t r a d e n t a t e l i g a n d s d e r i v e d f r o m e t h y l e n e d i a m i n e , e.g. s a l e n a n d a c a c e n , h a v e p r o v e d to b e e x c e p R E

R E

2

2

t i o n a l l y v e r s a t i l e i n c o o r d i n a t i o n c h e m i s t r y a n d c a t a l y s i s , w e h a v e fo c u s e d m u c h o f o u r effort o n t h e c o r r e s p o n d i n g d i i m i n o d i p h o s p h i n e s a n d diiminodiarsines derived from phosphino- a n d arsinobenzaldehydes a n d a variety of diamines. Discussion T h e C a r b o n y l p h o s p h i n e s . T h e arsino- a n d p h o s p h i n o b e n z a l d e h y d e s a r e t h e e s s e n t i a l s t a r t i n g m a t e r i a l s for t h e p r e s e n t w o r k a n d d e s e r v e c o m m e n t . T h e s e l i g a n d s , m a n y o f w h i c h w e r e p r e p a r e d first Scheme

I.

E = P, R=Ph,n = l-3 E=P, R = Me,n=l E=As, R=Ph,n = l

Alyea and Meek; Catalytic Aspects of Metal Phosphine Complexes Advances in Chemistry; American Chemical Society: Washington, DC, 1982.

18.

HOOTS E T A L .

Chelating

305

Agents Scheme II.

iminophosphines PPh

PPh

2

+

RNH

CH = NR

CHO

diamines


monoamines

-NH C

H

3

2

2

2

S

NH

2

*J3 by S c h i e m e n z a n d Kaack, can b e synthesized i n ca. 5 0 % overall y i e l d from the c o m m e r c i a l l y a v a i l a b l e o - b r o m o b e n z a l d e h y d e i n three steps (see S c h e m e I) (5). T h e p r o d u c t s a r e i s o l a t a b l e as a i r - s t a b l e , b r i g h t y e l l o w crystalline materials ( P h A s C H C H O is pale y e l l o w ) that are c h a r a c t e r i z e d r e a d i l y b y I R (v — 1 6 9 0 c m ) a n d H - l N M R (7(P,CHO) - 7 Hz). 2

e

co

4

- 1

Monoiminophosphines. As illustrated i n Scheme II, P C H O con denses w i t h a w i d e variety o f s i m p l e a n d f u n c t i o n a l i z e d mono a m i n e s . Studies o f the M o ( O ) derivatives o f several o f these l i g a n d s demonstrate that they efficiently d i s p l a c e C O from M o ( C O ) affording (chel)Mo(CO) o r / a c - ( c h e l ) M o ( C O ) d e r i v a t i v e s (4). S i m i l a r , b u t bimetallic, complexes can b e obtained from t h e ligands prepared b y c o n d e n s a t i o n s w i t h n o n c h e l a t i n g d i a m i n e s s u c h as m - o r p diaminobenzene. e

4

3

I n m o r e recent studies, w e have d e m o n s t r a t e d that this condensa tion reaction allows one to readily introduce chiral functionalities into the p h o s p h i n e system. For instance, ( - ) - 3 - p i n a n e m e t h y l a m i n e read i l y c o n d e n s e s w i t h P C H O a n d A s C H O t o afford t h e c h i r a l i m i n e s ; these i m i n e s also m a y b e r e d u c e d t o the c o r r e s p o n d i n g s e c o n d a r y a m i n e s u s i n g N a B H . T h e efficacy o f these l i g a n d s i n a s y m m e t r i c catalysis is b e i n g e x p l o r e d c u r r e n t l y , a n d i n v i e w o f the w i d e variety o f n a t u r a l l y o c c u r r i n g c h i r a l a m i n e s , o u r m e t h o d o l o g y is e x t r e m e l y promising. 4


306


D i i m i n o d i p h o s p h i n e s . T h e a l d e h y d e P C H O c l e a n l y condenses w i t h e t h y l e n e d i a m i n e i n r e f l u x i n g e t h a n o l to afford t h e o f f - w h i t e d i i m i n e , e n = P . T h i s l i g a n d r e a c t s r e a d i l y w i t h m o s t m e t a l i o n s afford i n g d e r i v a t i v e s i n a v a r i e t y o f g e o m e t r i e s as s h o w n b y X - r a y c r y s t a l l o g r a p h i c a n d s p e c t r o s c o p i c s t u d i e s (6).


2

A n e x a m p l e o f ( p s e u d o ) t e t r a h e d r a l g e o m e t r y is p r o v i d e d b y t h e Cu(I) complex, [Cu(en = P )]C10 . T h e structure from an X-ray study is d e p i c t e d i n F i g u r e 1 f r o m a p e r s p e c t i v e t h a t c l e a r l y s h o w s t h e ex p e c t e d s k e w e d e t h y l e n e d i a m i n e b a c k b o n e ( v i d e infra). T h e corre s p o n d i n g Ag(I) d e r i v a t i v e has the same g e o m e t r y j u d g i n g f r o m the s i m i l a r i t y o f the H - l N M R a n d I R spectra o f the Cu(I) a n d Ag(I) complexes. S q u a r e p l a n a r a n d five-coordinate d e r i v a t i v e s o f e n = P a r e f o u n d for t h e d i a m a g n e t i c y e l l o w [ N i ( e n = P ) ] and brown [Ni(en = P ) B r ] . A m o s t i n t e r e s t i n g f e a t u r e o f t h e s e c o m p o u n d s is t h e i r e l e c 2

4

2

2

2

+ 2

+

Inorganic Chemistry

Figure

1.

Structure

of [Cu(en = P )] with thermal at the 50% probability level 2

+

ellipsoids

drawn



18.

HOOTS E T A L .

Chelating

307

Agents

Inorganic Chemistry

Figure

2.

Structure

of Mo(en =

P )(CO) 2

3

t r o c h e m i s t r y , w h e r e i t is s e e n b y c y c l i c v o l t a m e t r y t h a t b o t h t h e n i c kel(I) a n d nickel(O) derivatives o f en = P are accessible v i a reversible 2

couples i n acetonitrile. I n a n a t t e m p t to p r e p a r e c o m p l e x e s w h e r e t h e e n = P l i g a n d is c o o r d i n a t e d t o a n o c t a h e d r a l m e t a l i o n , w e e x a m i n e d i t s c h e m i s try w i t h molybdenum(O). T h e r e d m o l y b d e n u m c a r b o n y l derivative M o ( e n = P ) ( C O ) is f o r m e d i n h i g h y i e l d f r o m M o ( C O ) (see E q u a t i o n 4). W e h a v e s h o w n n o w t h a t t h i s c o m p l e x c o n t a i n s o n e u n c o o r d i n a t e d p h o s p h i n e m o i e t y i n a d d i t i o n to the facially b o u n d P - N - N segment o f the c h e l a t i n g agent. T h e P - 3 1 { H - 1 } N M R c l e a r l y s h o w s t w o s i n g l e r e s o n a n c e s at 3 4 . 8 6 a n d - 1 6 . 1 5 p p m v s . H P 0 a t t r i b u t e d t o t h e b o u n d a n d u n c o o r d i n a t e d p h o s p h i n e s , r e s p e c t i v e l y . T h e s t r u c t u r e (see F i g u r e 2) is i n i n t e r e s t i n g c o n t r a s t to a n o t h e r t r i d e n t a t e e n = P c o m p l e x , [Cu(en = P ) ( f - B u N C ) ] C l 0 prepared from the reaction o f [Cu(en = P ) ] C 1 0 w i t h a slight excess o f i - B u N C . I R s p e c t r o s c o p i c data i n d i cated that the i m i n e s w e r e i n e q u i v a l e n t i n this c o m p o u n d . T h e X - r a y 2

2

3

e

3

4

2

2

2

4

4



308

s t r u c t u r e (see F i g u r e 3) r e v e a l e d t h a t t h e i s o n i t r i l e h a s d i s p l a c e d one i m i n e w i t h the formation of the tridentate e n = P chelate w h i c h c o n t a i n s a nine-membered chelate ring. T h i s c o m p l e x is l a b i l e a n d t h e f - B u N C e x c h a n g e c a n b e b r o u g h t w i t h i n t h e N M R t i m e f r a m e o n l y at - 6 0 ° C . C e s s a t i o n o f t h e e x c h a n g e b e t w e e n t h e Ν sites, w h i c h w o u l d r e s u l t i n a n o n e q u i v a l e n c e o f t h e p h o s p h o r u s d o n o r s , is n o t o b s e r v e d 2

e v e n at - 9 0 ° C b y P - 3 1 N M R . T h e geometry o f the chelates i n the t w o tridentate e n = P c o m plexes c a n be r a t i o n a l i z e d neatly b y c o n s i d e r i n g the s p a c i a l restraints o f t h e o c t a h e d r o n a n d t e t r a h e d r o n . I n t h e f o r m e r , t h e c o o r d i n a t i o n sites are a c c o m o d a t e d c o m f o r t a b l y b y adjacent six- a n d five-membered che late rings whereas the greater l i g a n d - m e t a l - l i g a n d bite angle o f the t e t r a h e d r o n s t a b i l i z e s t h e m o r e flexible s i x - a n d n i n e - m e m b e r e d c h e l a t e r i n g s e q u e n c e (see F i g u r e 4).


2

Mo(CO)

e

+ en = P

2

Mo(en = P )(CO) 2

3

+ 3CO

(4)

C h i r a l D i i m i n o d i a r s i n e s . T h e facility o f the i m i n e formation a l l o w s for s t r a i g h t f o r w a r d i n t r o d u c t i o n o f c h i r a l s u b s t i t u e n t s i n t o m u l t i d e n t a t e l i g a n d s c o n t a i n i n g soft d o n o r s . T h i s s y n t h e t i c r o u t e is p r o m -

F i g u r e 3.

Structure of [Cu(en = P )(t-BuNC)] + with the thermal soids drawn at the 50% probability level 2


ellip

18.

HOOTS E T A L .

C

Chelating

309

Agents

P,

N,

Mo(en = P )(CO) 2


Figure 4.

3

Selected angular

parameters

for en = P

structures

2

i s i n g for p r e p a r i n g s t e r e o s p e c i f i c c h e l a t i n g a g e n t s for l o w - v a l e n c y m e t a l i o n s . T h e H - l N M R s p e c t r a o f [ C u ( e n = P ) ] C 1 0 (35° to - 5 3 ° C ) a n d [ C u ( e n = A s ) ] C 1 0 (35°C) i n d i c a t e t h a t t h e s e c o m p l e x e s a r e u n d e r g o i n g r a p i d i n v e r s i o n a b o u t t h e m e t a l i o n as i n d i c a t e d i n E q u a t i o n 5. I n a s m u c h as t h e d i s p o s i t i o n o f t h e Ε • · · Ν ( Ε = A s , Ρ ) c h e l a t e 2

2

4

4

(5)

Δ-λ

Λ-δ

r i n g s is d i c t a t e d b y t h e c o n f o r m a t i o n o f t h e e t h y l e n e b a c k b o n e , i t s h o u l d b e p o s s i b l e to fix t h e o v e r a l l c h i r a l i t y o f t h e c o m p l e x b y l o c k i n g the c o n f o r m a t i o n o f that b a c k b o n e . W e h a v e a p p r o a c h e d this p r o b l e m b y e x a m i n i n g the conformation b e h a v i o r o f t w o analogues of e n = A s . B o t h the X - r a y structure o f [Cu(en = P ) ] C 1 0 a n d the F i e s e r m o l e c u l a r m o d e l s i n d i c a t e that p l a c e m e n t o f a m e t h y l g r o u p i n a n axial site o n t h e e t h y l e n e b a c k b o n e o f C u ( e n = E ) w o u l d result i n sig n i f i c a n t l y u n f a v o r a b l e n o n b o n d e d interactions w i t h the a r o m a t i c s u b s t i t u e n t ^ , a n d p r e l i m i n a r y e x p e r i m e n t s c o n f i r m t h i s p r e d i c t i o n (see F i g u r e 5). ( R ) - l , 2 - D i a m i n o p r o p a n e e f f i c i e n t l y c o n d e n s e s w i t h A s C H O to afford t h e d i i m i n e R - p n = A s w h i c h w a s c o n v e r t e d d i r e c t l y to its c r y s t a l l i n e c o p p e r ( I ) d e r i v a t i v e , [ C u ( R - p n = A s ) ] C 1 0 . F o r refer e n c e s , t h e l i g a n d e n = A s a n d its c o p p e r ( I ) c o m p l e x h a v e b o t h b e e n isolated a n d characterized. T h e H - l N M R spectrum of [Cu(R-pn = A s ) ] C 1 0 d i s p l a y s t h e c o m p l e x i t i e s e x p e c t e d for its l o w s y m m e t r y (see F i g u r e 6), w h e r e t h e m o s t i m p o r t a n t f e a t u r e is t h e p a i r o f r e s o n a n c e s for the n o n e q u i v a l e n t i m i n o protons. If this s p e c t r u m w e r e the w e i g h t e d a v e r a g e o f r a p i d l y i n t e r c o n v e r t i n g d i a s t e r e o m e r s (see E q u a t i o n 6), t h e 2

2

4

2

+

2

2

4

2

2

4


310


A-[CU(R-PN=AS )-A|

Catalytic Aspects of Metal Phosphine Complexes - American

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