As a statement of 'the primary purpose' of Kant' philosophy, if it had one (just one), this seems implausible.
Something closer to the truth would be that Kant sought to combine rationalism and empiricism but even this is not quite right. Both rationalism and empiricism had irremediable flaws in Kant's view. None the less each contained elements of truth which could be transformed and incorporated into what Kant eventually presented as his Critical philosophy. ('Critical', briefly, because it was set out in Critiques.)
Kant's main grouse was that rationalism sought and claimed knowledge of a non-empirical reality - God, for one thing in Descartes' case. Empiricism in contrast sought to derive all knowledge ultimately from experience. For various reasons Kant believed this to be a false account; only if filtered or structured by 'categories of the understanding', not themselves in any way derived from experience, could sense impressions cohere into anything that amounts to experience. The experience of space and time also requires 'forms of intuition' by which the understanding can experience anything spatially or temporally.
It's a long story but Kant's fundamental concern is to show how the Critical philosophy alone can explain how everyday and scientific knowledge is possible. This concern had nothing directly to do with ethics. Or at least its central motivation was not ethical; Kant was here working principally as an epistemologist.
Kant did intend in his major epistemological (and metaphysical) work, The Critique of Pure Reason (1781/ 1787), to include an examination of the principles of ethics. This was actually accomplished mainly - only mainly, because other, later works were also relevant - in the Groundwork of the Principles of Morals (1785) and The Critique of Practical Reason (1788). Ethics was of vital interest to Kant, and certainly no mere add-on to the other work. Opposed to ethical subjectivism, he argued that ordinary moral judgement - Kant takes morality as he (thinks he) finds it - can be objective but only if it contains an a priori element - an element not derived from experience. This element is one of rationality which branches out into the categorical imperative and its various formulations. When Kant insists that we must act in such a way that it is logically possible for everybody else to act in the same way, this idea is not something we can acquire from experience. How could be perceive this ? Yet nor is it rational' in the manner, say, of a Cartesian clear and distinct idea detached from action. But it is rational - practically rational - because it involves consistency, the consistency of everybody's being able to act in the same way.
Kant had a nexus of concerns. These interlocked within and between texts and ethics was always of profound importance. But I think it is an impoverishment of the Critique of Pure Reason to read it purely or even mainly as a prolegomenon to ethics.