Phosphorus Chemistry - American Chemical Society

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86 Cyano Anions of Dicoordinated, Tricoordinated, Tetracoordinated, Pentacoordinated, and Hexacoordinated Phosphorus A L F R E D S C H M I D P E T E R and F R A N Z Z W A S C H K A Institut für Anorganische Chemie der Universität München, Meiserstrasse 1, D-8000 München 2, FRG

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W I L L I A M S. S H E L D R I C K GBF, Mascheroder Weg 1, D-3300 Braunschweig-Stöckheim, FRG

Cyanoligands may change the properties of the center which they are attached to quite d e f i n i t e l y . In particular they reduce its basicity and participate i n an eventual anionic charge. This is i l l u s t r a t e d by the pseudohalide ions E(CN) , n = (7 - group number of Ε ) , i n accord with the "cyano displacement p r i n c i p l e " . They are found i n the first short period for n = 1 to 3 and also in the second short period for n = 1: n

C(CN) " 3

N(CN) ~

OCN~

p(ao ~

SCN" C I "

2

2

F~

The dicyanophosphide ion which continues this series has now been synthesized by reacting phosphorus tricyanide with dialkylphosphites (R = CH , C H ): 3

P(CN) P(CN)

3

3

+ +

2

HPO(OR)

5

2

+

Na,KPO(OR)

Et N 3

+

-»

Et NH P(CN) ~ 3

+

+

2

Na,K P(CN) ~ 2

+

NCPO(OR>

2

+

NCPO(OR>

2

While however neither its triethylammonium salt nor its a l k a l i salts are stable i n solution, the salts of crown ether-alkali complexes are stable as such and i n solution. In the reaction which we have found, phosphorus tricyanide behaves as an interpseudohalogen, (NC) P-CN, with "positive cyanogen" which i s taken over nucleophilically by the d i a l k y l phosphite anion. With reverse polarity however, phosphorus tri­ cyanide reacts with the dialkylphosphite i n the absence of a base: 2

P(CN)

3

+

HPO(OR)

2

+

HCN

+

(NC) P-PO(OR) 2

2

The dicyanophosphide ion is bent, as is the isoelectronic molecule S(CN) . A transfer of charge into the cyano groups i s expected from charge density calculation and is demonstrated by N-coordination to the cation i n the crystal (Figure 1). It i s also in accord with the observed wider CPC-angle (95°) and shorter PC­ -distance (170 pm) and the lower CN and higher PC stretching fre2

0097-6156/81/0171-0419$05.00/0 © 1981 American Chemical Society

In Phosphorus Chemistry; Quin, L., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1981.

420

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PHOSPHORUS CHEMISTRY

Ζ Figure L

[18]Crown-6-KP(CN) . 2

In Phosphorus Chemistry; Quin, L., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1981.

86.

SCHMIDPETER

ET AL.

CyOTlO

421

Anions

q u e n c i e s as compared w i t h t h o s e o f P ( C N ) and CH^PCCN)_. The d i ­ cyanophosphide i o n could thus react a m b i v a l e n t l y , but t h e n u c l e o p h i l i c i t y o f phosphorus outweighs by f a r t h a t o f n i t r o g e n . P ( C N ) 2 may be u s e d t o i n t r o d u c e t h i s g r o u p b y n u c l e o p h i l i c s u b s t i t u t i o n . T h i s r e a c t i o n h a s b e e n u s e d e.g. t o p r e p a r e t h e d i cyanophosphino d e r i v a t i v e s of h e t e r o c y c l i c c a t i o n s , which i n t u r n may be r e d u c e d b y p h o s p h i t e a g a i n . The r e s u l t i n g compounds a r e b e n z i m i d a z o l o n e s and q u i n o l o n e s i n w h i c h t h e PCN g r o u p a s a n o v e l pseudochalcogen takes t h e p l a c e o f oxygen. 3

R

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R

pcn

CC>

κ

I

CN

R

P(CN)?

Cl°

PCN

- KXOEt),CN -a* P(CN)£

They o c c u p y a c o n n e c t i n g p o s i t i o n b e t w e e n t h e h i s t o r i c p h o s p h a m e t h i n e c y a n i n e c a t i o n s s y n t h e s i z e d b y D i m r o t h a s t h e f i r s t -P=Ccompounds, and t h e d i c y a n o p h o s p h i d e a n i o n ( a n d t h e y show i n d e e d i n t e r m e d i a t e s p e c t r o s c o p i c and s t r u c t u r a l d a t a , F i g u r e 2 ) . I n a m e t a t h e t i c r e a c t i o n t h e s e i o n s a f f o r d s a l t s w h i c h h a v e t h e same c o m p o s i t i o n a s t h e above compounds. They a r e s t a b l e a s c r y s t a l s but s u r p r i s i n g l y r e a r r a n g e i n s o l u t i o n even a t room t e m p e r a t u r e e.g. on a t t e m p t e d r e c r y s t a l l i z a t i o n . The exchange c o u l d p r o c e e d v i a a diphosphetane betaine. A t y p i c a l r e a c t i o n o f h a l i d e i o n s i s t h e i r c omb i na t i on _ w i t h a halogen molecule to give the l i n e a r t r i h a l i d e ions . In accord with i t s postulated pseudohalide character, the dicyano­ p h o s p h i d e i o n a d d s b r o m i n e and i o d i n e a t room t e m p e r a t u r e t o g i v e a n i o n s o f X^ t y p e w i t h P(CN)« a s c e n t r a l member. The c r o w n e t h e r sodium s a l t s o f these h y p e r v a l e n t a n i o n s , dicyanodihalophosphates ( I I I ) , c a n be i s o l a t e d i n c r y s t a l l i n e f o r m . P(CN),

P(CN) X 2

2

(-»

P(CN) X 2

+

X )

S u r p r i s i n g l y t h e r e a c t i o n does n o t l e a d j u s t t o t h e d i c y a n o h a l o p h o s p h a n e s ( w h i c h i s t h e c a s e f o r X = C I ) . The i o n s w i t h X = B r o r I do n o t d i s s o c i a t e i n s o l u t i o n a s i s a p p a r e n t f r o m t h e c h a r a c t e r ­ i s t i c upfield shift of the Ρ-NMR s i g n a l (-165, - 1 7 2 ) . A d d i t i o n o f cyanogen bromide o r i o d i d e i n s t e a d o f halogen gives the tricyanohalophosphates(III), X = B r , I . P(CN)

2

+

XCN

P(CN) X 3

P(CN)

3

+

X

In accord with t h e i r s t a b i l i t y mobile e q u i l i b r i a l y i n g f a r t o the

In Phosphorus Chemistry; Quin, L., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1981.

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422

PHOSPHORUS CHEMISTRY

s i d e o f the products are e s t a b l i s h e d from phosphorus t r i c y a n i d e and c r o w n e t h e r sodium c h l o r i d e , b r o m i d e o r i o d i d e , f r o m w h i c h t h e p h o s p h a t e s ( I I I ) c a n be i s o l a t e d a s c r y s t a l s . In s p i t e o f t h e i n t e r e s t i n h y p e r v a l e n t p h o s p h o r u s ( I I I ) com­ pounds a s s u b s t i t u t i o n i n t e r m e d i a t e s , l i t t l e i s known a b o u t t h e i r g e o m e t r y . I t i s p r o p o s e d t o b e ψ-trigonal b i p y r a m i d a l w i t h t h e l o n e p a i r e q u a t o r i a l a n d t h e e n t e r i n g n u c l e o p h i l e and t h e l e a v i n g g r o u p o p p o s i t e t o e a c h o t h e r i n a p i c a l p o s i t i o n s . No s t r u c t u r e determinations of a hypervalent, four-coordinate phosphorus(III) s p e c i e s has s o f a r b e e n d o n e , h o w e v e r , t o p r o v i d e a m o d e l f o r t h i s t r a n s i t i o n - s t a t e g e o m e t r y . We c a n now p r e s e n t t h e s t r u c t u r e s o f t h e a n i o n s P(CN) B r " ( F i g u r e 3 ) , P(CN) C I ( F i g u r e 4 ) , P(CN) B r ~ ( F i g u r e 5 J , and P ( C N ) I ~ ~ . W h i l e t h e f o r m e r two show t h e expected ψ-trigonal b i p y r a m i d a l c o o r d i n a t i o n w i t h c y a n o l i g a n d s i n t h e e q u a t o r i a l p o s i t i o n s and a n a l m o s t l i n e a r B r - P - B r and C l - P - C N a r r a n g e m e n t , r e s p e c t i v e l y , t h e l a t t e r two a r e d i m e r i c , s h o w i n g a n u n e x p e c t e d ψ-octahedral c o o r d i n a t i o n o f P ( I I I ) . The t e t r a c y a n o p h o s p h a t e ( I I I ) w o u l d be t h e c o n c l u d i n g member i n t h e s e r i e s P(CN) . I t forms indeed from phosphorus t r i ­ c y a n i d e and a phospRonium c y a n i d e , b u t decomposes a b o v e -10 C: 3

3 P(CN)

3

+ 3 CN~

->

3 P(CN) " 4

-*

P(CN) " 2

+

P

C

N

2

2 10 1Q "

The two s a l t s f o r m e d i n t h i s d e c o m p o s i t i o n c a n be i s o l a t e d and s e p a r a t e d . A s t w c t u r e d e t e r m i n a t i o n shows t h e d i a n i o n ( F i g u r e 6) to c o n s i s t o f a t h r e e - c o o r d i n a t e d i c y a n o - and a s i x - c o o r d i n a t e p e n t a c y a n o - p h o s p h o r u s c o n n e c t e d b y a C ^ u n i t . Whether c a r b o n o r n i t r o g e n i s t h e b r i d g i n g atom t h e r e i n i s s t i l l open t o d i s c u s s i o n . 3

Figure 2.

Molecular

structure of

cyanophosphinidene-N-methylquinolone.

In Phosphorus Chemistry; Quin, L., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1981.

SCHMIDPETER

ETAL.

Cyano

423

Anions

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86.

Figure 4.

Molecular

structure of the anion

P(CN) Cl~. 3

In Phosphorus Chemistry; Quin, L., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1981.

424

CHEMISTRY

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PHOSPHORUS

Figure 6. RECEIVED

June 30,

Molecular

structure of the anion

PC N 2

l0

1981.

In Phosphorus Chemistry; Quin, L., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1981.